Depends on the situation.
If I'm talking to my true, real friends, then sure, we'll talk about it. I would never judge them for having or wanting kids; why would they judge me for not? If they do, they're pretty lousy friends. My best friend and I don't agree on everything; so what? That doesn't mean we can't be our honest selves with each other.
Really think about it: would your friend pester you into changing religions? political affiliations? sexual orientation? owning a pet? moving? changing careers? liking a food you hate? Of course not. Think about the usual garbage that people say to the CF and consider acceptable behavoir.
Now reverse it: Would you ever pester and prod your friend over his/her decision to have kids? Would you keep telling them how much better their lives would be without them? Would you tell them that they may not want an abortion or sterilization NOW but SOMEDAY they will and that they will regret not having had one for the rest of their lives? That maybe when they're more mature they'll change their mind? That other people's kids might be great, but it will be different when it's their own? That they haven't truly lived unless they haven't had kids? That their lives are meaningless because they have kids? That they're never going to know what it truly means to be an adult if they have kids? That they'll never know love if they have kids? That they're being selfish for having kids? That they shouldn't have kids cuz they're parents don't want grandchildren? That they're marriage is meaningless with kids? That there must be something wrong with them? That they're going to die pathetic and alone? Of course you wouldn't. Cuz that would make you a lousy friend (and perhaps a lousy person). So why is it okay that someone treat you with that kind of disrespect? Aren't your feelings just as valid? Don't you deserve as much consideration as you give to them?
When it comes to meeting new people that I think I could make real friends with, I'm honest about it. If we can disagree but have a conversation about it anyway, then great. If we can't, then we can be acquaintances perhaps, but why would I want to devote myself to a relationship in which I'm not respected for all of me or in which I have to hide part of me or pretend that part of me doesn't exist?
If I'm in a work-related place/function, I minimize conversation about everything personal. I don't choose my co-workers; I'm stuck with them. So I act accordingly in order to minimize annoyances from people whom I have no choice but to see 50 hours/week. If asked, I'll answer politely and move on.
If I'm in a place where I won't ever meet these people again, then I either a. avoid the subject altogether because I don't want to be bothered or b. speak bluntly cuz what the hell.
