> Do you think average human cares about "our species is going extinct" stuff?

Yes.

> If not, why couldn't they be happy at the same time?

The same reason you can't be happy if I stick a fork in your eyeball.

You'll get back to a similar 'happiness' baseline after a while but we can all agree you would've been better off with 2 eyeballs. If you go 'well, akshually' as you are doing now, I'll stick a second fork in your remaining eyeball.

If you mind me sticking forks in your eyeballs, you should also mind society that makes people not have children.

Whatever 'well, akshually' you invent - it's deeply unconvincing.