It's quite simple really. When combating anti-Semitism was tough, when it involved going up against the world's most powerful nations and the wealthy and powerful within Western societies, it was the LEFT that was clearly in the forefront against it.
Now that genuine anti-Semitism in Western society consists mainly of some losers with spray-cans, we find fearless right-wingers joining the fray.
The fact that "anti-Semitism" has been expanded to mean criticizing Israeli imperialism, makes right-wingers even more happy, because they get to take the side of a bully and imagine that they're fighting a worthy cause at the same time.
It's kinda like how US repugnican youth imagine they're fighting for "democracy" against "Islamo-fascism" by writing blog-posts at home while their overstretched armed forces are murdering civilians in Iraq and Afghanistan.
Pathetic Loserdom to the nth degree.