I think it is perfectly ok to hate shitty parents. But it seems to me that many people really hate the children, not their parents. Many of them also tend to generalize and hate all children in a simple children-bad manner. I often see people who are not afraid to say they just hate children. I find those people in all groups - some of them are childless, some of them are good parents and some are the shitty ones. It seems to be the popular edgy thing to say.