The question is often between what is art and what is simply marking their spot.
Banksy's refreshing for being much closer to art in intent.
When an image is represented in a public setting. Does that image take away from, or give to the public ?
How can such images be considered vandalism if the image increases the value of the property ?
When art is stolen from a gallery, it is theft. If art is stolen from the public, it is sold. Who is at fault ?
"When an image is represented in a public setting. Does that image take away from, or give to the public?"
It depends on how they go about it. If the image compliments the scene, that's different from people who just throw their tags everywhere like they're a dog marking the neighborhood.
"How can such images be considered vandalism if the image increases the value of the property?"
It's being done without permission is how. I wouldn't like someone tagging up my property without consulting me first, and painting over it costs money.
"When art is stolen from a gallery, it is theft. If art is stolen from the public, it is sold. Who is at fault?"
I don't get this part.