I don't have kids and don't plan to have. Nobody is forcing me not to have kids, in fact the opposite. I am the black sheep of my family and social circle, people look at me weird for not having kids (not that I care).
The problem with asking people to live responsibly is that it hasn't worked so far. Ever tried asking a meat eater to reduce a tiny bit of their meat consumption? Another issue is that even if it worked, it will take a long time for people to change their habits. We should of course educate people about responsible living, but we should also remember that it is a long, hard process.
I don't know what the solution is, but we are at a point that we should try everything we can think of, including asking people to have less kids, live responsibly etc etc