Artistic directors of some 60 of the country's most prominent nonprofit theaters responded swiftly and forcefully to the firing last Thursday of Ari Roth, a playwright and a.d. of Theater J, a prominent Washington D.C. company funded by the Jewish Community Center. In their letter, the chiefs -- including Oskar Eustis, who leads New York's Public Theater and organized the letter campaign with Tony Taccone of Berkeley Repertory Theatre, along with Andre Bishop…