> Thanks to this attitude birth rates have collapsed in most of developed world and we have 2 pensioners for every child.
Rather thank the politicians who sold you a pyramid scheme as a pension system.
> Between this and climate catastrophy,
If you argue with climate catastrophe, you should rather argue for decreasing the number of people (which includes avoiding having children) to decrease the CO2 footprint.
Reducing the population by having a low birth rate is good. But mathematically it cannot be so forever. To maintain a non-decreasing population you need 2 children per woman on average, doesn't matter if your country has 10^4 or 10^8 people.
Immigration is only a temporary solution, it may not be a reliable solution by the end of the century. Global birth rates are falling and QoL is slowly improving, reducing the incentive to immigrate.
Thanks to productivity gains in the last 100 years, that's not a problem. We have a solid amount of people not working, we don't have a shortage of workers in general, we're lacking high skill workers, and workers who are willing to do shitty jobs. We can solve the high skill issue with education, and the latter with better wages for e.g. elderly care and nursing.
So the government should redistribute wealth via taxes to incentivize having kids. Why would an individual employer be expected to take on that burden? Not to mention the arbitrage opportunities it opens up.
Because you want society to exist, and keep existing. More concretely: you want to have people around you until you die, and it'd be kind of immoral to demand they kill themselves when you kick the bucket. So they will want people around until they die. And so on and so forth.
TLDR: you want children to exist now.
And that's ignoring how our society works, because the way pensions work you want about 4 times as many children as old people. That's a lot of kids we haven't had, but the alternative to that is way more taxes. Clearly we don't want way more taxes, so 4 times as many kids it is. Except we're not doing that either, and ... uh ... I guess we're hoping God will save us?
TLDR: you want children to exist now. And, actually, you should want the number of kids to roughly double from what we have now (in the US, in Europe, a minimum of 4x is needed)
Why not rather: you don't have such a time-intense hobby such as raising kids, so you deserve more income.