Profanity filter
There's also a problem with automated profanity filters: they're prone to abuse. It's pretty common for people using excessive profanity to change characters or add spaces or other punctuation to break up bad words and get around software that looks out for it. This puts you back in the situation of needing to have actual people with actual brains and eyes looking things over -- at which point the software is useless.
Some software tries to get around this, but it just makes the problem worse. Back in my BBS days, I ran afoul of a group that used a profanity filter in its chat room. The problem was, it removed all the spaces from your text before scanning for bad words -- and it was very unforgiving. It would give you a strike if you typed in, for example, I wish it would rain. It wouldn't even tell you what you did wrong, just that you were bad. On the third strike, it would ban you from the group for a day.
An automated system would only be as good as the people who designed it, and it would be subject to their opinions as to what is bad. The people determined to use that sort of language would find ways around it anyway, and making it more restrictive to counter them would have the net result of penalizing innocent users.