This is not true. You would be gobsmacked to find out how many people judge the shit out of you for not having kids.

In my experience, these childfree sorts who group together have done it because they are or were constantly criticized for their choices by people whose voices mattered to them; family, coworkers, friends. They find a place where they can belong and let their frustrations with others out where they won't be criticized, and the catharsis of being able to be themselves seems to turn into a drug to them.

I had a vasectomy at 25. I'm 37 now. It's a toss up over what I appreciate doing to myself more; vasectomy or lasik. Both have made my life almost immeasurably better for the things I want to be better. I also got lucky in that my family was pretty understanding of my desires - or at least enough that they didn't want to get into an argument with me about it. I was lucky that I had the right combination of (grand)parents passivity and a past history of extremely strong-willed sarcastic rhetoric that they didn't want to make it a big deal. Over time, they fully accepted it. So, while being child free is definitely me, I never felt like I had to find peers who understood me; I wasn't being questioned constantly or held to task for my decisions, so I didn't feel like I needed to be around people who understood me. Those who didn't didn't matter, and those who did matter either did or didn't say anything negative, so I didn't need to care. I never felt like I was under attack or having to justify myself at the drop of a hat every time I interacted with someone.

My wife, meanwhile, has had a far greater struggle with her family. The critical commentary is effectively nonstop; it isn't, actually, but it can happen at any moment, so she is always at Defcon 2. This is exhausting for her. She hasn't turned to childfree groups for acceptance, but it isn't hard to empathize why someone would. Being around people who understand your decisions and where you can say all the things you wish you could tell your mother, grandmother, aunts and cousins is a pressure release valve.

I can see this in other groups too; anyone who is marginalized or mistreated by society as a whole or people they are close to, they find a safe space and can let their frustrations at the mistreatment they receive out. It helps them stay true to themselves at times when they may otherwise feel forced into a role they do not want to be in by any society that values conformity to specific values and behaviors more than anything else.

Then when people like you or I come across these groups who are doing things contrary to who we are or what we believe, we recoil in horror at the rhetoric. I'm a hetero cisgendered white dude who makes tech money in a tech city. I'm part of the problem to so many people, and get painted with a pretty broad brush. This upsets me sometimes, but I always remind myself that there's a reason why people are doing this, and it really has nothing to do with me in specific. It's a coping mechanism, and I defer judgement on them until the real test; If, after I treat them as valued individuals with valid feelings and emotions and an equal worth to myself, if they don't feel the same vitriol toward me as their rhetoric would imply, then we're good. If they still want to write me off, then I think they're jerks and move on as well. But that doesn't mean that they're wrong for finding a place to belong and vent their feelings. That's just humans being humans.