I'm afraid I don't quite get that second sentence. I take it as axiomatic that anti-semitism is a bad thing. (So does Joseph Masser evidently - it's worth reading that article, and not just the quotes I picked out).

It's clearly impossible to be against anti-semitism and at the same time anti-Jewish. The broader definition just means that it similarly impossible to claim to be against anti-semitism and to be anti-Arab.

Words change (eg "What is folk?"), and there is no reason to accept the definitions imposed by the 19th century racists who invented this one.