What are reasons graffiti should be legal and reasons graffiti should not be legal

Graffiti should be legal because it can used for educational purposes. For example, doing graffiti in a art class. Also, it represents art, which is a big factor in human society. Graffiti shouldnt be legal because some people may jeoperdize other people's property. For example, spray painting on the back wall of a house that isnt permitted. Also with all the symbols that can be made, groups could be formed based on marking territory with graffiti art.