People get a lot of gratification in raising children. Something that people without children can't really understand fully. I know I didn't understand it until I had children. You're building (for lack of a better word) something that will outlast you, the original legacy. If you spend time helping people in need, I mean really spending time and energy, not just donating or virtue signaling, it's similar. An example would be teaching or coaching; being a big brother or adopting a child; being a good aunt or uncle; mentoring even, to a lesser degree, etc. Taking care of and benefiting someone who depends on you doing it.

>reduces humanity back down to level of any other simpler life form. Eat, fuck, die, repeat.

Though humans (most) are civilized and intelligent, we're still a great ape.

>It's a belief I find hugely depressing.

Why? It's our nature.

Plus I think what parents do a poor job expressing to non-parents is that kids are fun. Like, they're a lot of tedious work, especially in the first three or four years, but they're also like the most entertaining fun thing out there. You know how it's fun to be around people who are really having fun? It's like that, but often.

Just as a top-of-mind example: All through my adulthood, I really disliked Halloween. Just not my thing, too much pressure to pick a creative costume, then go to a tedious party. But last night I had such a great time taking my five-year-old trick-or-treating. Because it's so new and exciting and fun for her, and that's infectious! But that sort of thing happens a lot.

That's what the metaphorical "cake" is. But that doesn't mean "that's it, there is no other joy to seek in life now", like the parent comment seems to be inferring. It's just one source of joy, but one that is hard to capture any other way.

I think you misunderstood the comment. "Cake" in this thread is just a metaphor for "that which brings you joy". It is inarguably the case that peoples' children are one of the things that bring them joy.

None of the rest of what you seem to have read into it is written there.