Many, if not most people, use insults to get a reaction but not to debate or show any point, the reaction could be simple things such as showing frustration or explaining yourself when it talks back to a one-sided interest on the topic. Naturally, on topics that they are out of touch with and don't like to think about they will use whatever comes first to their minds which is usually the widespread vapidly empty platitudes, in response to anything conflicting with the pushing of that narrative it is repeatedly resorted to ad hominem which replaces confrontation of arguments with blame of character, they only wish to "help" in this way because nothing else tries to force their narrative and thus doesn't get what they want from you. Of course, their forced pushing for a narrative that pleases them involves no substance and therefore they have no interest in reflecting on any truth or questionings of assertions that are beneficial to them.
They do not have any mind that's capable of understanding anything in relation to CTB or that's interested in the mind that is you unless they can substitute your thoughts with their own which isn't the same as being interested in your mind, much less interested in the topic of CTB. Talking to such an individual on this subject, as I have with one friend, is a sure way to be insulted, invalidated or otherwise be preached on pro-life-style, all under the guise of good intentions that somehow entitles potentially being further blamed for exposing this. One other and very different friend was respectful but knowing his limits kept it quite distant and brief, so while you may want to vent or to know how your way of thinking compares to others you know, there is not much to it but a lot of flawed rationalizations and because of that it's generally a useless bother that I can't recommend, at least on a forum like this one it isn't utterly opposed but welcomed to write in favor of one's own interests and choices.
I'll note here that appealing to anyone whose views oppose, oppress, invalidate, belittle and condemn CTB while promoting manipulative beliefs that perpetuate pointless life in prestige is nothing I wish to do. I think dignity and freedom is found in transcending conventional ego and not in trying to ease its sense of powerlessness.
My interest on this subject lies not with them but with confronting the reasoning-wise shallow, uninterested and ignorant nature in their dismissive arguments.
The portrayed stupidity that's pointed to in CTB is often primarily the seemingly completely unknown effects death has on you, on a person's mind/perspective that is, not taking into account any basis for what can be expected or what basis would be had for doubt. Burden of proof lies on proving what is and not on what is not, you wouldn't do anything relatively simple to get or avoid something much larger because you can't disprove such a claim when the claim can't be proved, that warrants reason for why people, even those with the agnostic view that it could be like anything to be dead, doesn't follow any religion to ensure not being eternally punished in case that religion is true. I deduce this as meaning that it's unreasonable to account for skepticism based on the impossibility to relate instead of realism based on science. It's identified that the brain and the mind are correlated. If the brain is damaged then the function of the mind may be damaged as well. The mind is generated by the brain and is therefore annihilated with the brain's full cessation of function, to not experience would resemble permanent dreamless unconsciousness, no other interpretation has any proper scientific basis and is therefore not credible.
While some evidence isn't absolute proof, it still proves more than no proof, which is a point that's often overlooked in favor of appeal to ignorance where the lack of absolute proof is used to dismiss any basis for any assumption on something controversial whereas absolute proof is almost never used on whatever people consider crucial matters otherwise, such as what career choices would be preferable or whether to reproduce or not. This dismissal is then frequently used to label any suicidal person as stupid and cowardly for not dealing with the, to them, non-issues at whatever point the suicidal person is on in a normal life which must be related to like normal and for choosing to die to leave it up to random chance that it gets better for whoever chose to die even at the expense of the assumable interests of that person's assumable loved ones. As previously explained in this text, the result of death on one's mind is not up to random chance and as for what is or is not a non-issue just like what matters or has importance, it's subjective, especially regarding that which you have the most unassailable title to which is your own life and person. The interests, conditions or actions of others, outside of consented confined give and take relations, warrants no service in return for any unshared objectives.
Another central argument claiming that CTB is stupid is of course the widespread vapidly empty platitude that "life is a gift", asserting that having been conceived is an inherently good opportunity granted by one's parents. I assert that no one neither can nor should gratefully admire anything they don't value no matter how much anyone else values something or wastes it, no one should feel the same about life in place of someone else. Parents generally reproduce to fulfill their need of a family life and thus want their children to be happy with that. Pointless needs and almost limitless potential for suffering is granted the children, but this is a sacrifice the parents are willing to make, unknowingly or not since this is, so far, of course a given it's very socially acceptable generally in society. It's sometimes thought that people complain too much and don't acknowledge what they can enjoy enough, but what they won't acknowledge is that people feel differently about what's important to acknowledge. This view that "life is a gift", is like a modern version of the religious view that considers everyone's lives as property of God which must be accepted and worshiped, it's something I regard as manipulative lies because they want to gain by having not any fewer but always more slave-like workers and consumers which leads to conflict and prolonged suffering, revolt in favor of purpose over performance is what I think would be superior. Coincidental sacrifice of life is no better than protest against life either. I think all of this is to only care about life in itself rather than the people who are alive because of the propagation of others. Fundamentally life cannot be a gift since one's existence must precede what one is given.
All those who attempt to CTB many times shows that it's not some easy act to be easily brushed off rather than thoughtfully confronted, the decision to CTB is the biggest most personal one possible and the act of following through with it does often involve the biggest risks of failure that may induce permanent crippling body and brain damage. It isn't just killing yourself, society often portrays it as too much to ask for, that's why in the currently few countries where euthanasia is provided the criteria tends to be very restrictively specific, such as a terminal illness and assuredly dying within six months.
Cowardice depends on how emotional resistance interferes with attainment of interests and not having any certain interest such as in living is not cowardice. For example, someone who wants to murder anyone and picks an easier victim because it's easier is cowardly, but no one who does want to murder a specific person is cowardly for not picking the most difficult target possible to murder since that wasn't the point. Someone who doesn't want to kill anyone isn't cowardly for not daring to do so, unless an imminent lethal threat is presented that by absolute necessity has its killing prevented by killing and where survival of the victim is of greater interest than to not kill, then it would be cowardly to not kill.
If there was a button for instant death or a choice presented to you between waking up and dying every time you were about to awake, much more people would choose to die, showing that many do not go through with CTB in conflict with their best interests because it's easier which is what cowardice is. Not acknowledging the interest of another is nothing but a manipulative reverse psychology trick, using what tends to be an unshared perception of worth and prestige in an attempt to taunt someone into serving their interests entirely separated from the point of why and what the individual in question would want. Therefore, those using this tactic may say that CTB is choosing to take the "easy way out" or to "give up", since it contributes, at least symbolically, to humanity's extinction which in their obviously reactionary perspective is inherently bad. If a set goal is never chosen or doesn't apply anymore, then ceasing all further efforts with a greater final effort is not to give up. Acceptance of the unacceptable is what it means to give up and to put in the least admirable effort, unlike its very conventional perception I think it's living with everything in conflict with one's best interests without any plan for desirable change, instead of not enduring insufferable struggles in itself when it serves nothing worthy.
No one wants to play a losing game for the sake of it and pretend it's not. There is no point in working to consume entertainment to be amused as much and as many times as possible like it's about some high score that's portrayed as the magnificent opportunity when it's anything but to someone who desires purpose over performance. I bet that if humans designed their own biology they'd still make births forced, preach futile pursuits and have suicide further oppressed and condemned, trying to prevent the act like a justice system with no concern for justice but only what penalties are used. They rather pretend the choice over the continuation of one's own existence is something to be happily repressed. Since consent cannot be established upon anyone's conception, that warrants not manipulation but transparency, reason for creating others or openness about ultimate futility while rendering it unwarranted to reason for one's own choice over one's own existence.
Given that an interest with certainty is had in ceasing to be, it's neither cowardly nor stupid at all, as much as others with absolute bias to infatuation with amusement may like to pretend otherwise.