Yeah. But UC Davis had a bridge outside of town, kind of hidden by vegetation. While there was very little graffiti in the city, that bridge was an open space for graffiti and spray-paint art. I like having public places like that where vandalism is implicitly allowed, so that the rest of us can have nice property.
Banksy can paint on my property because he has something to say. Someone just writing their name needs somewhere else to work on their artistic voice.
Yes, I also like the idea of dedicated public space. It brings out really cool graffiti. For example, I remember seeing a huge mural on the side of an apartment building in Warsaw.
It's not "because he has something to say", but rather "because it's worth a shit ton". I'm sure there are many graffiti artists who have more interesting ideas than Banksy does. Would you be alright having an insightful tag on your wall that's worth nothing more than the insight?