Without addressing your other characterizations, I will point out that the Palestinians are Semites. So if elements of the left are supporting the Palestinians, they still can't be called "anti-semitic".

Yes, they can be. While the etymology of the word "anti-semitic" stem from analyses of the various Semitic languages, today the word means hatred or discrimination against Jews. Not all speakers of Semitic languages generally (which include not just Palestinians, but all Arab-speaking peoples) - just Jews.

Sometimes words shift meanings over time. If you say that someone's job performance was awful, it's not a compliment - if you say it was awesome, it is. Even though originally the words were synonyms. And if you say that someone's job performance is awful, you're insulting them. Pointing to the archaic and/or discontinued original use of the word doesn't erase the existence of the current, modern meaning of it.

The same is true of the term "anti-semitism." Despite the origins of the word, in modern usage it is a reference to hatred or prejudice against Jews (whether they speak Hebrew or not), not Arab speakers.