Why is my desire to be childfree so upsetting to people, yet it's totally cool for people with kids to complain about their kids?

I just don't get why my childfree choice is so offensive to parents and people with kids. Also, parents complain about their kids left and right, and nobody bats an eye, like "Oh, it's just venting, it's fine!" But if a childfree person says ONE negative word about parents or kids, everyone loses their shit. I have always thought that parents complaining about kids is way more offensive than anything the childfree have ever said.