Good tagging is art though. A tag back in the day was either well executed with a distinct style, or the next guy covered it up.

Besides, tagging was sorta rarely just initials. Wasn't exactly unheard of, but your tag was typically a thing of its own.

And yeah, there's a lot of overlap between graffiti as art and graffiti as vandalism, but the people that made a hobby, then art form, out of it weren't just scrawling initials.