Every single left-wing march flies a lot of flags as well, only they are different flags.

Political movements in general don't seem to be particularly immune to flag shagging, only the colors vary a lot.

But I am pretty sure that Banksy means right-wing flag worship as well. He is a master of "provocative conformism" and wouldn't produce anything that would get him into a real risk of controversy. His art is very fine-tuned to the sensibilities of the English and American chattering class; same recipe for success as Paul Krugman or Malcolm Gladwell.