... well you have two different issues here
one is tagging and one is bombing
personally i dont think they should be mixed together because I believe one is a form of urban art and one is straight out vandalism
what it comes down to is that taggers are out there to deface all and any surface with their signature - a scrawly piece of graffitti that denotes someones alter ego
a bomber goes out and pulls a masterpiece of colour design and style and adds a new urban form of art to a wall that screams out for anything that isn't beige, white or grey
IMO the tagger should be penalised and the bomber should be celebrated by providing more walls for these designs to be showcased
but hey .... everyone has an opinion, right??