I hate the sort of graffiti which is just 'Debbi luvs Bazza' written in felt tip. I've seen kids hanging round train and bus stops making their rubbishy felt tip pen marks before now and ended up arguing with them to not do it because it looks awful, but they probably just come right back as soon as I've jumped on my bus.
Spray painted arty graffiti can be really nice though. The ones who use that tend to be more serious, as it obviously costs more to buy the materials and they need to take the time to work out how much space they've got and what they can draw in that space.
I've seen some amazing murals and can only wish my best to the artists that created them.
I've no knowledge of this particular case, though. Were they persistently graffiti-ing the same property, or writing inflammatory stuff or something?