First off, swearing does belong in mature content along with blood and drug use. Mature content doesn't refer to maturity in the same way as it would in real life. The mature content that reflects mature thinking is above a child, they just wouldn't understand it in the same way. It's different than showing them something that's straight up shows peoples arms being lopped off, lines of cocaine, and rampant profanity. You want to censor kids from the things you don't want them to see. They'll understand mature thinking at their own pace. You shouldn't try to protect them from that.
Also wanted to add that I really don't think there's any relation between how much someone swears and their vocabulary. A lot of the people I know who swear enjoy the kings English just as much, if not more, than anyone else. I tend to swear like a sailor and I, not to be boastful, do know a few more words than someone who never took studying language seriously.
Ever notice how no one is really ever surprised or offended about swearing? They always seem to be offended on the behalf of other people.
I did adopt this view from someone else. A like is in it for anyone who knows who.