It’s hilarious that you’re downvoted because asking them to move has never failed in my experience. Given I’m in the Midwest and there’s the whole “Midwestern sensibility” stereotype, but I don’t think anyone here is different from anywhere else.
Most people who do this either don’t think about the fact they’re blocking the whole aisle or they don’t realize you want through. A simple excuse me will let them know
It all depends on context, imo. People should generally leave other people’s private property alone. But if it’s an ugly cinderblock wall downtown, some kind of drab piece of infrastructure, and the graffiti artist is actually making an effort to make it look good - it can be public art