"Let them cry it out" being neglect isn't a strong opinion, it's the literal definition. A lot of neglect and abuse has been socially normalized but that doesn't make it not that: thankfully corporeal punishment has been outlawed in most Western countries although many parents and educators still struggle understanding that punishment itself is ineffective.

That children who are subject to any given for of abuse or neglect don't "seem" harmed by it, doesn't make it harmless either. I think we've all heard people who hit their kids argue that "my dad hit me when I was a kid and it didn't do my any harm either" and don't accept that as a justification anymore.

I'm not saying people who do this (because they are taught to do it) are bad people. I'm saying what they are doing is bad and that there are training centers who sell neglect as "sleep training" (which can refer to other things) are bad.

I don't know why you think "do you even have kids" is a gotcha but yeah, I have kids, I also have nephews and I have friends who have children. Would you insist that someone isn't allowed to speak on whether it's okay to hit your wife if they aren't married, too? That someone telling you off for leaving your dog in the car on a hot day has no right to criticize you because they don't own a dog themselves?