All graffiti is low-level dissent, but stencils have an extra history. They've been used to start revolutions and to stop wars. Banksy History
Should graffiti be judged on the same level as modern art? Of course not: It's way more important than that. Banksy Art
Graffiti's always been a temporary art form. You make your mark and then they scrub it off. Banksy Art
There's obviously nothing wrong with selling your art - only an idiot with a trust fund would tell you otherwise. But it's confusing to know how far you should take it. Banksy Trust