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.
I suppose it's true that the left-wing equivalent is the Palestinian flag, or the centrist equivalent is the Ukrainian flag, however this usually comes in the form of a sticker or the odd flag flown from a house window here and there, rather than a row of flags hung from every lamp post on a street.
Quantity has quality all of its own. Although many different causes use flags for promotion, the obsession that certain elements of the English right have with the English flag is at a completely different level.
Choosing a traditionally suited man as the standard bearer adds a formal banality to the blindness (to my eyes).