I hear you; the copyright case especially shows that he is no paragon of anti-capitalism. But I think it's worth maintaining that (1) some things are worse than other things and (2) motive matters and (3) imperfect people can still make good points.
I have never, ever felt like a piece of Banksy's art, or any original piece of visual artwork for that matter, is being shoved down my throat. They're quiet, static, relatively low in number, and easily avoidable & ignorable. I've never felt distracted or distressed because my local coffee shop has a new mural on their wall, and nobody has ever forced me to walk through an art museum in order to get to the grocery store. On the other hand, advertisements are loud, moving, insanely numerous, and totally non-optional. My local subway and subway stations are plastered in advertisements; if I want to transit anywhere, I must endure them.
Plus, the motives are different! Sure, Banksy or $artist_name likely want folks to find their art appealing and then compensate them somehow, via buying copies, commissioning new art, spreading their reputation, whatever. But advertisers do not care if you found their ad appealing; they just want you to buy their product. In fact, many ads are purposely obnoxious or abhorrent just because it's an effective way to bring your attention towards their product. How dystopian is that?
And yes, there's some irony in Banksy, as someone who occasionally benefits from copyright law, to be making this point. But that doesn't make him wrong! And, it'd be far more ironic if, I don't know, Sergey Brin or someone else who use hugely benefited from advertising and copyright law were making the point.