Because the alternative is just letting your gene line or even the whole species die? Theres also some people that still believe, and probably can succeed, that they can raise kids resilient enough to face those challenges and brave enough to tackle them. If in 40 years governments finally wanna do something about climate change, they're gonna need some younger hands and boots on the ground to get it done.
Not all of us were raised in a decent life. There are people who grew up in war, slavery, and all sorts of worse shit. They eventually escaped and made a decent life for themselves. Why wouldn't they believe their children could do the same?