It is reasonable to call Galloway an anti-semite, but it doesn't follow that everyone who does it does so "reasonably", ie from a left-wing or even minimally consistent anti-racist point of view.
The evidence seems to suggest that the attacker is a right-winger and an anti-Palestinian chauvinist. That is relevant information, but information you seem determined to ignore.
The AWL has fought for decades against the left promoting George Galloway, but he is not a fascist like Nick Griffin. You could draw many comparisons between Stalinism and fascism, but there are important differences in terms of their supporters here. If right-wingers attacked a Morning Star seller we would defend the Stalinists against physical attack while condemning and fighting them politically.