I won’t call it a sin, if you have no other option, and many don’t, Public schools are the education of last resort. Sadly though far too many people foolishly treat them as education of first choice.
Public Schools are to education what public housing is to housing. Yes, not all kids and teachers in public schools are problems or bad, most are decent, however just like in public housing, those decent majority are run roughshod over by the indecent minority.
Sometimes it would be better for a child to be completely illiterate and innumerate than to ever set foot in their government K-12 school. There are schools that are that bad.