I think Siegal was being a little oversensitive. The movie was a humorous spoof of Starsky and Hutch, so instead of having the usual Italian mobster or black or hispanic drug gangs that Hollywood seems to do ad nauseum, they decided to go with a Jewish drug lord.

They could have gone even further by making it an Amish drug lord, but the Jewish angle worked. The absurdity of the Bat Mitzvah scene just added to the humor.

Larry David does plenty of Jewish humor on Curb your Enthusiasm as he did on Seinfeld. I don't feel that if the effort turned out to be unfunny that it would qualify it as being anti semetic. After all, humor is a subjective thing. Hate isn't.

This review of "Starsky & Hutch" in the paper L.A. Citybeat provides an idea of what Siegel was talking about:

"Given the months of debate and accusations prior to its release, the first question that must be dealt with is whether 'Starsky & Hutch' is indeed anti-Semitic. What, for instance, are we to make of the fact that the villain, drug kingpin Reese Feldman (Vince Vaughn), is Jewish? Or that a central scene takes place at his daughter's bat mitzvah (rendered in the broadest, least respectful light)? Or that Starsky (Ben Stiller) crashes that sacred event by affecting a thick accent and calling himself 'Mort Finkel'?"

I think that from that description alone, it's clear that Siegel has a point. While the idea that Jewish characters, religious/social events and even accents are intrinsically humorous is a longstanding cliche, a lot comes down to the execution. No one would say that slick, somewhat dishonest agent Ari of "Entourage" is offensive just because he's Jewish (and, in fact, did business at his daughter's bat mitzvah). But being Jewish is an integral part of his character -- of course, many actual Hollywood agents (and screenwriters, for that matter) are Jewish. But more than that, he's genuinely funny. And that makes all the difference.