Ethics is define as the the principles of right and wrong that are accepted by an individual or a social group, so if the artists accept it why should it be punished?

I think it shouldn't be punished even tough your decisions do affect other people. Yet I think is a good way of expression and it is not harmful.

crappy ones are crime.

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I wish the world was flat like the old days
Then i could travel just by folding a map
No more airplanes, or speedtrains, or freeways
There'd be no distance that can hold us back.

but doing it on walls that don't belong to you is crime..

but it is art and beautiful never the less,
I say stick to paper or your own walls