Multiply it times a billion. One Banksy is tolerable, a million people graffiting their opinions everywhere would be truly awful. Therefore what Banksy is doing is immoral.
I disagree with the scale multiplier being a metric of morality. If one ice cream truck drives down my street, it puts me in a good mood even if I don't want to buy any ice cream from them. A continuous parade of ice cream trucks would be maddening. But that doesn't mean the ice cream truck driver who actually exists is behaving poorly.
One Jesus of Nazareth is tolerable, a million people preaching their opinions everywhere would be truly awful. Therefore what Jesus was doing is immoral.
A million people do preach opinions today, and did in Jesus' time, it's not horrible.