No it isn't. For two basic reasons. Graffiti is a form of art, and many truths are written on walls. Many of those politically correct citizens hate it though. I believe it happens because they cannot handle the truths written on them, and they've been told that, destroying someone else's property is a crime.
I walk a lot through the day and I come across many walls. Either they have a graffiti on it, or some message as well. Those messages are often true, and I agree with almost all of them. Many people I know agree with them as well, but there are certain categories of people who freak-out when they see someone writing or drawing on a wall. Which are those categories of people? Let's see:
The most obvious I think. But it's their job to punish people who write/draw on walls, so if they catch someone doing such a thing they are like F*ck yeah, more job for me. One step closer to my promotion. Such a simple-minded thought, coming from simple-minded people like cops. No cop is smarter than average because if they were, they wouldn't choose to do this extremely shameful job. Have you got no shame wearing this uniform?
2) Fascists (Right-wings)
Those who tilt on the right, when it comes to the political spectrum, are almost always having fascistic thoughts. Others have more, others have less. But if someone calls them with their name (fascists) they'll whine like little babies and usually say I'm not a fascist, I'm a patriot. The last phrase is very common actually. These kind of people is very loved by the cops, and they love them the same as well. So these people are the ones who are more likely to report someone who writes/draws on a wall. Also I should mention, it's not a coincidence that fascists never express their thoughts on walls. Why do you believe it happens? Think a little bit.
3) Lawful citizens (sheep)
Those kind of people might not be so active politically, or not even bother at all, but the problem here is they're NOT so neutral. They do what the society tells them to, and they're those who have this kind of mentality. I don't bother with politics, but I think it's better to follow society rules. There you have it. Society suggests that people who write/draw on the walls are evil. So what those kind of people will do? Report you. Being naive can be really dangerous. More dangerous than it seems to be.
Sure there are more categories, but those are the 3 main ones.
Anyway I said what I wanted to say and before I finish I want to say 2 things:
For people who do this: Keep on doing it. If someone stops you or reports you it's their problem.
For people who are against it: You are the perfect slave to the system. Keep supporting it, by punishing those who speak the truth. Hope one day, you'll realize how wrong you are.