In a democratic society, if citizens are particularly concerned about the aesthetics of public property, they can make their views known to the relevant authorities and elected representatives, and it could even become an election issue. I think that's far better than citizens fighting with paint.
Broken window theory. Once a few things have graffiti, it will quickly proliferate including stuff that isn't exactly aesthetic.
Any cursory googling will yield several papers debunking the broken window theory for you.
Sorry, I used the term incorrectly. I'm not suggesting that graffiti increases crime, only that the presence of graffiti encourages more graffiti.
I live in Japan which is usually free of litter, put a few empty beer cans on the floor and come back 24 hours after and you will have a trash pile. I don't need a paper to tell me that.