"It really undermines the sense of community when vandals deface public spaces and community centers and apartment blocks."
I much prefer graffiti in my field of vision than corporate billboards. In SF I don't even notice the graffiti, maybe because most of it is hard to read and understand? But I do notice the huge huge billboards over every thoroughfare with the stupid corny messages.
The people in these communities feel the opposite of you, especially since a lot of street art is murals capturing some local culture e.g. see Clarion Alley in San Francisco, a lot of very explicit messages of community.
Then why is Clarion Alley covered in graffiti that hundreds of people a day come to look at? Why is said graffiti often applied by residents?
City ordinance is not an accurate reflection of the desires of all subsections of a city. It's a reflection of the desires of the ruling caste, whose needs sometimes, but frequently don't, align with those of "lower" castes.
A bench is a great place for a nap, unless the mayor happens to see you sleeping on one, gets scared, and calls the cops about it.
It really undermines the sense of community when vandals deface public spaces and community centers and apartment blocks.