Yes, I believe that surveillance camera's should be used to prevent vandalism on outdoor works of art, especially if the item is worth a lot of money. Although sadly in the world that we live today there are always going to be people who are going to not care and ruin other peoples things. With surveillance camera's up, or without - some people just don't care.
By installing surveillance equipment where it can be seen in and around outdoor exhibits would aid in preventing vandalism by making vandals think they are being watched. Individuals may feel their privacy is being invaded, they are in a public place where privacy is already at a minimum. Lastly, unless individuals are planning on committing a crime they shouldn't have any reason to complain that artists want to protect their lively hood.
Yes, I think surveillance should be implemented to prevent vandalism on outdoor works of art. You wouldn't want someone to vandalize indoor works of art, and if they did then you'd want compensation. Why should we differentiate between indoor and outdoor art? While I don't think it's feasible, I still think it's a really good idea.
We all usually think that art work outside IS vandalism but in some cases they are considered art! In this case, I do believe surveillance should be installed as no one should destroy someone else's art, you should respect it. The fact that you're ruining someone else's art IS vandalism and in that case you should be responsible for your actions.
You clearly do not know who Banksy is or what he does to even suggest that surveillance would be the way to go.
Frankly that is all that there is to that particular notion. It is amusing however to see someone suggest that stopping a vandal against a vandal with security cameras is a good idea.