There’s no reason that it can’t be both. Whether or not something is a crime is just a matter of what laws are on the books, which is completely independent of whether or not something counts as art. Your other questions are way to broad to be answered with a simple yes or no. Should people get arrested for making art? Not just for making art. But if someone decided to go on a killing spree and call it performance art, I don’t think there would be a lot of wringing of hands over whether arresting them was censorship. Should people run free after ruining other’s property? This assumes that graffiti ruins whatever it is added to. Banksy’s Girl with a Balloon sold for £500,000 (almost $640,000 right now). I bet the shop owners didn’t consider their wall to be “ruined” after that. But just because graffiti doesn’t necessarily ruin someone else’s property doesn’t mean anyone should feel free to tag anything they want. In short, I don’t think any of these are the “real question.” The real question you seek would need to have a much more nuanced understanding of the issues involved.