There is absolutely nothing wrong with not wanting kids, and choosing not to procreate definitely doesn't mean you need to end your friendships with the people that did. If you've got friends that have kids, it might be difficult to comprehend the long list of ways in which their lives have changed (and no one can fault you for that) but it's important for both you and your friends to remain supportive of one another. One way to remain supportive is to avoid being too opinionated about the things you can't talk about if you're not a parent.
I know, what ever happened to freedom of speech, right? Of course you have the right to speak your mind, but if you value your relationship with your friends that have kids, there are certain conversations that you should just avoid if you, yourself, aren't a parent. I am embarrassed at some of the smug things I said about parenting before I actually had kids of my own, thinking I knew what was "right" or what I would do before I was in a situation that made me eat my words and apologize to far too many mothers. Trust me, I've made the mistake of commenting on parenthood when I wasn't a parent, and it did nothing but make a mother feel worse and me feel, well, pretty dumb.
There are things that all new parents want their friends who don't have kids to know, just like there are things women who don't want kids are tired of hearing. I think there's some middle ground between the two valid experiences, where we can all come together and support one another without making everyone feel defective or "wrong" or anything other than valued. So, for the sake of the people who are on my side of the parenting fence, here are a list of things you should just avoid talking about if you don't have children. Leave it up to the professionals, right? (And by professionals, I mean the exhausted parents who are just trying to figure out how to get through each day without screaming.)