Χίλια μπράβο! A thousand bravos for all your effort!
Barbarians will always be barbarians, but is our duty as members of this society to try educate and make people care about things other than themselves.
Oh! And just like you said, there are ugly grafittis, but there are real works of art. I spent my univerisity years in Thessaloniki and next to the ugliness and pure wish for destruction (driven by rage and disapointment) you could see quality paintings that actually turned old, deserted buildings into beautiful canvases and run down neighbourhoods into street galleries. Too bad I don't have any photos to show you...
Probably one way of judging whether it is art or desecration is if the person who puts it there has the blessings of the owner of and/or community around the site. This would be a first prerequisite IMHO.
I would agree on that, but: the final outcome could still be real art despite the "artist" having asked for permission or just took the initiative and "created" on someone else's property. What if Picasso (or any other established artist) was a graffiti artist and filled the streets with murals at will? Wouldn't his creations still be art?
What I am trying to say is that we should be trying to cultivate respect and good manners. It is an indication of how educated people are. A talent is wasted if the artist acts like an animal within the society they belong to.
I just remembered this mural by @romanie, street mural, Ibiza 2016
And this is just an example of the graffitis in Thessaloniki (I found the photo on the internet, but I have walked past this building and it is very beautiful):
