I'll grant you a point in that countries like China are so overpopulated that government has to mandate and regulate the amount of reproduction going on, but the family unit has been the key societal pillar since ancient days.
In ancient Japan, for instance, not even the Emperor could go against the word of a Father when it came to the treatment of his family. (Found this out by reading
Shogun, by James Clavell).
And while adoption is an admirable pursuit, parents should not be denied the right to create a child who is their own offspring.
As for your comment about overpopulation causing the decay of the planet, you are probably right that this should be another topic, but since the two are connected I think we can just roll with it.
Overpopulation does have a drain on our resources. There is no getting around that and I'm not going to try and argue with it. Global warming I'll fight you tooth and nail over, but let's save that for another thread.
Still in this case I don't believe the ends justify the means. Reproduction is a natural part of life. What we
should do is have better education for people out there so they can weigh the options before having kids. Also we need to have better access to contraceptives.
To some religious people who believe that making contraceptives hard to get will stymie a teenager's sexual drive, I have one thing to say: Good luck with that. It won't happen. Teenagers will still have sex and some will get pregnant.
I don't believe in abortion as a method of birth control, and its not fair to punish the unborn child, so let's just make contraceptives free and easy to acquire (for my full stance on abortion, let's wait for another thread).
Attacking on these two fronts we can reduce the number of accidental pregnancies and children abandoned by their parents and also make sure that the parents who decide to have kids will be fully aware of the expenses and risks involved. It wouldn't be immediate, but over time it would reach the end goal you're seeking, sora-mage.