I think what makes me more tolerant of this kind of behaviour is the "harrumphing" it inevitably elicits from a Certain Tendency. Graffitiing is a sign, a symptom of something going on in the society. You can harrumph and grump all you like about how it's just "not like it were when I were a kid"...and in doing so, you'll completely miss the point. Both points. Because it was like that, you were just fortunate enough not to see/notice, and it is a sign that someone is pissed off with their position in society. Which usually ends up meaning that there's something wrong with society, not necessarily with the people doing the protest/graffiti/etc.
And, all too often, the reason that this is the case, is because we're listening a bit too hard to the harrumphers, and not nearly hard enough to what the people on the streets are saying, via whatever means.