I agree with you that there is a lack of perspective for some people, for example solely wanting to ctb over having a smaller penis size and having that one issue as the primary motivator also makes no sense to me either. Especially when there are many women who will openly admit it's not a deal-breaker for them. No offense to the guy in question, of course, but a thread title like that can come off as a non sequitur with no context.
However, I feel like those views are probably indicative of some deeper issue which is not always articulated, perhaps ongoing rejection or feelings or worthlessness that have persisted due to lack of success in the dating game or hateful comments from other people about his body and looks. Truthfully it's not something I can relate to even as someone who struggles with my own appearance and bodily dysphoria at times, because many cosmetic things can be alleviated with enough disposable income, and I'd consider looks maxxing way before jumping the gun to ctb. To me, it's a last resort.
Yet, men like that who can be impressionable to strong beliefs due spending a lot of time online are bombarded with content that reinforces harmful ideas that they won't ever have skin in the game when it comes to romance due to a factor like their dick size, which probably makes someone less receptive over time to hearing any sort of thought that's in conflict to that if that's all they're exposed to, but it's hard to say when we only know little pieces of info that others choose to share.
It's kind of similar to how I view the philosophers as you put them, there tends to be some sort of unspoken issue underlying the crux why they find death appealing and beautiful, since it's inherently a taboo point of view. As annoyed as I got with some of FC's posts at times, especially how she would speak down to others, I've known for awhile now that she used to be on a tinnitus form before SS and if I had to bet (though it's only speculation) the reason why she made similar, almost romanticising, odes to death ad nauseum is because of her long term medical conditions and autism. Will we ever know? Probably not, since she never really shared that personal side of her life in her posts, which is why it seems to come off as insincere or lacking in perspective in a lot of the content, all context is missing.
A person with a good life wouldn't feel so drawn towards death as a concept, I feel like. Unfortunately, many people don't really articulate why they believe these things, but I tend to give them the benefit of the doubt that if someone is espousing very pessimistic philosophy that they have to experience some sort of anger or pain to come to those views. Or have a propensity towards ruminating on some of the more depressing things in the world (I saw this often when I used to read antinatalism stuff, people would constantly post really doomer-y, often ragebait, articles about terrible accidents, wars, climate change, and whatnot to remind everyone that life sucked all the time, which was like pure poison to some people who needed to stay away from that to keep sane)
As I've gotten older (and crankier) there's a lot of things I don't really relate to either, but I just tend to stay away from posts I don't like these days, unless it's something I can contribute to. I still feel bad for people like FC even if I disagree with some of her more extreme views, and she might consider me a dumb pro-lifer at the end of the day.