I get really frustrated when (some) parents imply you can't have an opinion on raising children if you've never been a parent yourself
Every adult who has ever lived has had the experience of being a child. Even if (maybe, especially if) the adults responsible for looking after you fucked it up, or were non-existent, you still understand the parent/child dynamic (or lack of it) from the perspective that matters most—the child.
You don't need to be a parent to recognise what shitty parenting and neglect looks like