There are at least three problems with people who don't try to think logically about this:
First, they don't think about life itself, which is a broad topic but once you know how shitty is biology for example, you wont risk having a defect newborn (even if its very low probability, it can happen and you can't do anything in many cases). Biological body is shit and contains a lot of potential risks not controllable by anyone. Religious and programmed people will bypass it by saying its fate and command of god or anything similar, also biology itself programs oneself to reproduce. But to the sufferer its a hell life and humans actually won't care, they'll thank God for themselves or anything similar and that's it. That's only about the shitty biological madness that people aren't aware and not to mention how medicine and biology itself evolved because of the death of many people, so people die in order for the rest of the species to advance more. What's the value of the life of someone who suffers only to be a material for learning for other beings. Once you consider the individual point of view in life, its always bullshit. This point will lead to other inherent problems in life which people don't think about and there are endless problems in life also like wars, economy or any single little thing that can be considered a problem. I won't continue here but let's assume that a human won't reach the scientific level for this and life is fine and dandy for them but, the second point...
Second, they don't realize how it is not a free choice usually (regardless of the question of free will), it is a completely full system made by humans that favors and enforces natalism and most of the times its not actually a choice. Religion and society oppress and limit sexuality which means the males usually are controlled by their dicks. Then they put absurd amount of economical obstacles which subliminally tells the person that if you need this woman and sex , you'll have to pay and pay, making the person indebted. Of course, they'll encourage marriage and reproduction in their companies and work systems, it has more advantages over the single, childfree one. One will get tempted to get the economical advantages, which on other hand creates another problem of fake and economical marriages that has no real love or emotions. But even if someone loves and wants a person, it will get muddled by financial problems in some cases but when that happens, its usually too late, the parents are indebted and probably hate each other but sometimes stay together because of children and society. And children themselves are already born and it can be a shitty life because their parents has the negativity of the system stained on them. The system doesn't care, it created money from the indebted parents and will have the potential manpower of children. But when some parents realize this, it can be very sad, some will change their attitudes towards the children but probably won't tell them how life is bullshit because its a mind blowing topic. Of course, not everyone is like this but we are talking about a dominant system worldwide that operates everywhere regardless of the political stance. Those who'll choose not to obey the system are extremely rare, so actually most of the times procreation happens, its because of social, beliefs and system conditioning rather than individual choice. So if someone is born because religion said so or because the society and the state wants more people to enslave, what is the value of a life where everyone is expecting you to be something like a robot and not being yourself. Humans lived like this for the whole humanity duration, you can see clear natalist examples in groups and tribes and how a child must be born to be the new leader or king. Also there is the example of military expansion and natalism, states wants to increase population to colonize the world and fight in wars (Facism in Italy for example), what's the value of a single life if it was made just for imaginary entities like states then living just for killing and fighting then dying at the end? All of those are examples of how life is just a rigged thing against humans and not a free choice type of thing. But do people change and make it better? No. They will still ignore all of this and continue like nothing is a problem. So we go to the third point..
Third, logically, one to find a contradiction in life value, one counter example is enough to prove. Otherwise to prove life is worthy, it would be necessary to check everyone's life and check if its worthy. Let's assume a child is born, then died in early childhood years in a war. What is the worth of life from the child point of view?
This can be applied to anything else, any sufferer can use themselves as a logical counterexample. One is enough as a logical example even if life has no sufferers and only one, it will logically makes any statement about how life is good wrong.
This also can be applied on parenting. Societies and cultures specially old traditions are full of crap that say parents are divine or whatever and a child must submit to them (in some cases even allowing them to do whatever abuse physically). So the saying parents are good or natalism has no wrong can be foiled by one counter example only. Some parents are trash and some kids will suffer, that's enough to prove and having some good parents and not a sufferer kid doesn't disprove how the thing is logically not in favor of natslism and parenting. If someone doesn't care about other cases? That's selfishness, like saying let everyone else burn but my family. You won't prove that families and natslism are good if you have a good family as it is all situational. But on the other hand, the sufferer can prove otherwise, because they suffered, as a counter example. The life from their point of view is hell. They can just accept that some people got it better, but do you think everyone just accepts their life to be trashed and see (regardless of meaninglessness) how they got pained and can't do anything. This is why shitty religions and ideologies comes to make the one more absurd and accept illogical parts of life. But when someone accepts illogic, that's absurdity and you can't talk with logic to any of them (which is how many people are in this planet). And there is no fourth point
