Last 2 guys, it's a simple mathematical problem. In Socialist Utopias the state takes from those who work and gives to those who do not. The baby boomers are retiring. They have not sired enough kids to take over the bills. This means less funding for more people, which means higher taxes and less payouts for each individual. Everyone loses. Matters of environment, ethics, lolcats and whatever else is entirely irrelevant. It's a problem that will bankrupt all of Europe even if there were no other problems, and it will take generations to fix if we started right now.
This isn't entirely true, the production rate is higher than before, even with less people.
So if you need less people to produce more stuff, it could be possible to solve this.
Also environmental problems and population growth are strongly connected, it's creating the upper limit that will break the exponential growth if nothing else does.
You've hinted at having more kids as viable solution, which clearly isn't the case.
and it's their fault for not having enough kids