Antisemitism is cultural.
Not necessarily. Since the traditional antisemitic canards rely on spinning Jews as rich and powerful, manipulative and sneaky, and with undue power over others, it appeals to worthless individuals of all stripes looking for a convenient scapegoat for all their own shortcomings. The disgruntled, the paranoid schizophrenics, those suffering from a Joan of Ark complex -- all concentrate their attention on Jews as there is already such a ready-made wealth of material out there for them to utilize.
As far as culture is concerned, it is often less a matter of culture than a mere PART of the culture. Leftists are increasingly hostile to Jews because it is fashionable and they are seeking approval from other leftists. The United states, as a whole, is not antisemitic, but levels of antisemitism run very high in the black community, fast increasing portions of the left, and a small vestige of the paleocon and white supremacist portion of the right. Since Europe is dominated by leftist politics, the levels of antisemitism run much higher.
I don't think it's as simple as "fashionable" but I actually agree with parts of what you say.
I think anti-semitism is cultural in large part. It's taught and passed on in a culture. That's why it has never completely disappeared.
I think anti-semitism is one component of a broader need to scapegoat and scapegoats will always be whatever relatively powerless minority exists. In addition, a minority that is seen to be insular, and outside of the mainstream culture, will be even more likely to be scapegoated. I don't see it as a left vs right situation. What I see as different is that it has always been the provenance of the right before, and now we are seeing it also in the left. The right is cloaking it in anti-Muslim rhetoric but the followers still spout the same old canards.
I think the fact that levels of anti-semitism are much higher in Europe is not because of leftist politics but because of history. Europe has had a strongly entrenched history of antisemitism - that resulted in expulsions, pogroms, lack of rights and forced conversions of non-Christians, in particular Jews. The US, Canada, Australia - while it's had anti-senmitism, never had that history. WW2 after all, was European.
But I agree it is a part of the culture - an ugly part, that is kept largely out of sight until stresses give it strength and voice.
Scapegoating a religious, ethnic or racial group is unfortunately very human. They are viewed as "outside" and when nationaism rises - outsiders suffer. It doesn't matter what group it is...it's wrong, dangerous and tragic.