I've never been shot down for it, but I'm very openly vocal about the fact that I don't want kids. Spending a couple of decades or more out of my own life to bring up others does not sound like something I want to pursue when I'd rather dedicate myself wholly to my career, my hobbies, and basically myself. I'd like to get married, too, but again, I'd want for me and my husband to just enjoy each other and our partnership, and not bring kids into it. I also don't want to pass on my genes and have to put up with what my parents put up with when I was little. And, obviously, if I don't want kids at all, I won't want them enough to bother adopting either.
Gotta agree with Charizard, there, too. The human population is ridiculous, and if anything it's helping matters when people who don't want kids don't procreate. People shouldn't have kids unless they want to and are prepared for it. It's no one's 'duty' to have them, especially now.