You explain:

The story of the Passion can be told without disparaging the Jewish people. Such an account is mandated by the Catholic Church as a result of the Second Vatican Council

Well, good. And happily, Mel Gibson's movie The Passion of the Christ was, indeed, such an account: It told the story of the Passion and it did not "disparage the Jewish people" to any reasonable interpreter. (I make no claims as to how unreasonable folks will interpret it.) And since you agree with the ADL that this (telling the Passion story w/o disparaging the Jewish people) is possible to do, merely noting that it's a passion play is therefore insufficient to prove the charge that it's antisemitic.

Another way to formulate such a charge would be to watch the film or otherwise learn a sufficient amount about what's in the film, and based upon this knowledge, point out the ways in which you think it disparages the Jewish people or otherwise violates the Vatican 2 proscriptions. I would be open to such arguments even if (as with those of AIS) I might find most or all of them wanting.

Alas, this option is not yet available to you....

Best,