People who bash and make fun of childless people
Whenever a woman makes a video about being 40 and childless or something along those lines, some comments will make fun of her, call her a cat lady, selfish etc.
The idea that the only reason people don't have kids is that they just want to party is a huge and often inaccurate assumption. Some people have fertility issues, others felt obligated to take care of sick family members and couldn't have a family of their own, others have psychological issues and knew they wouldn't make good parents. Some of the reasons that people don't have kids are actually the opposite of selfish.
Btw I think that certain childfree people are cringey too. (Like the ones who bash children all the time) However, those are a a tiny minority, dwarved by people who bash the childless with no context.
Also, I think it's a bit hypocritical how some have only one child when they could easily afford more yet they act superior to childless people and blame them for the birth rate problem. If you're concerned about birth rates why did you only have one kid?