Defacing public property is worse. It's toxic individualism and self-expression. If people wanted to put up a mural, they'd collectively vote to do so. In a proper society, graffiti artists would face public punishment from the collective.
In a “proper society” we could pass around the talking stick to reach consensus on a whole grab bag of things.
I’m not a tagger myself, but I do think there is something poetically democratic about people participating in the public forum in this way. At least, beyond the four-letter words and flying dicks, anyways.
"Democracy" isn't about individuals or small groups making their voices heard. That might be a necessary factor, but it's not the purpose. Democracy is about the majority having the right to create the kind of society they want to live in. Maybe people in Sao Paulo like the graffiti (or maybe not, since the ban on other types of visual pollution seems popular). But it's the majority's decision to make.