Yes but anti-semitism has been co-opted to apply only to Jews (erasure of millions of other semitic people, that is, people who speak a semitic language other than Hebrew) just like the Holocaust has come to mean only the Jewish victims of Nazi genocide, which is erasure of the 5 million other victims in the various groups that were killed by Nazis.

That’s an invalid (strikethrough: dictionary) etymology argument, and you know it. To clarify, when I said “antisemitism” I meant “a discriminatory attitude towards Jews” or something along those lines.

Edit: this is an etymology argument, not a dictionary one; most dictionaries probably agree with me. I don't know how or why the word antisemitism came to be used to refer to Jews specifically, but surely it's been this way for most of its history.
Either way, the most authoritative meaning of a word is that which was intended by the one who uttered it.