At some point in history, humans stopped being animals and created society/civilisation.
This society was largely designed to protect us from the harsh realities of existence as an animal on this planet. When someone dies, it is the community that protects you from death by carrying on the day to day necessities of life and giving people some sort of purpose to their existence. (however hollow that purpose may be - including just merely keeping people busy and distracted)
Suicide is seen as a threat to the very existence of society itself. It is a rejection of life, which is a bit like a self imposed exile from community/society... this is why there is such a militant pro-life faction who try to protect society from this threat. They are trying to prevent the spread of what they deem to be a dangerous idea. The idea that death is a legitimate life choice and a viable option for every person in society.
They will fight hard to make sure that suicide is never deemed to be a socially acceptable life choice.
That's my perspective on it for what it's worth. And they could very well be right in viewing suicide in this manner, but it still does not make militant pro-life tactics or behaviour correct... because ultimately every human being should have free will and autonomy over their lives. That should always logically include the ability and right to choose not to live at all. If that is a threat to society... then so be it.
