Below are excerpts from a fascinating essay written by a self-described non-Jewish Welsh Zionist (it's my understanding that there are many more black Mormons than there are Welsh Zionists) who started out in the usual place -- loathing Israel -- and then came to something more complicated. I only know Tom Doran from Twitter, but he seems like an interesting guy. Here is his analysis of the roots of left-European anti-Zionism:

American and Israeli accounts of anti-Zionism have a tendency to portray modern Europe as slouching towards a Bethlehem of Jew-hatred, with far-left and far-right combining to bring about a return to the 1930s. I wouldn't go that far. Anti-Zionism is certainly ubiquitous on the hard left, but in my experience is merely one component of a seamless, all-encompassing theory of the world that, if I may be cynical for a moment, revolves around three questions:

1. Which side is the United States on?

2. Which side has all the money/weaponry?

3. Which side, overall, has lighter skin?

Where all three questions generate the same answer, that answer is The Enemy. Where the answers are mixed or unclear, the result is abject confusion, as in the case of Syria. In the manner of a stopped clock, this formula will occasionally yield the correct position, as with South Africa (of which more later). More often, it's a first-class ticket into the moral abyss. In the interests of balance, I should point out that a nontrivial percentage of right-wingers make use of the same three questions with the results inverted.

Doran, who is himself a product of the left, is careful to note that many stridently anti-Israel European leftists are not anti-Semitic per se, but do make common cause with people who just don't like Jews:

I don't mean to suggest that genuine Jew-hatred is unheard of on the left, merely that cause and effect operate differently than many suppose. Once you've decided that Israel is an avatar of Western imperialism and Jewish supremacy, it's hard to avoid being drawn into a clammy underworld of paranoia in which mainstream, reality-based criticism cross-pollinates with, as the phrase goes, something much darker. An example that might be familiar to American readers is the sad case of professor John Mearsheimer. Once he'd identified Israel as the chief source of American foreign policy woes (with partner-in-Jew-baiting Stephen Walt), it was only a matter of time before he plunged into the gutter with an endorsement of notorious Israeli neo-Nazi Gilad Atzmon.

Read the whole thing, it's quite interesting, particularly his observations on what you might call Apartheid Substitution Effect, the desire of some well-meaning leftists to experience again the excitement of the anti-South Africa divestment movement of the 1980s. Also interesting to the headquarters staff at Goldblog is Doran's statement that a certain book about the Middle East opened his eyes to the complexity of the issue.