I think Graffiti is just a modern form of art combined with a bit of vandalism.
first, it's a way of attracting attention to your works as you might not have any other ways of doing that. second, if it's beautiful I don't have any problem with as we live in cities and we are surrounded by depressing grey buildings and it's goo if we have someone to make them brighter.
If it's not that beautiful it could fall under th'VANDALISM' category because it doesnt cater our need only making everything worse. That's what I think about it