This is a tag which started showing up here around February 2021. I've even added it myself importing some e621 tags
It seems to go back around 12 years to 2010ish according to https://e621.net/post_versions?commit=Search&page=29&search%5Btags_added%5D=bad_parenting
To me it just seems too subjective a judgment call. Like you would have some people call literally any instance of parent/child incest "bad parenting" for example. Or even other stuff like spanking, impeding masturbation, encouraging masturbation, etc.
Rather than see that show up increasingly everywhere it seems like a better idea to just nuke it to avoid potential differences in view over what is or is not good/bad.