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.