The US backing the Mujahedin in Afghanistan is not an 'accusation'. It's well-known fact. In fact, an entire movie (Charlie Wilson's War) was made based on a US politician's efforts to convince people in the US that arming and backing an Islamist group like the Mujahedin was a good way to counter the Soviets, despite the risks and unforeseen consequences:

https://www.imdb.com/title/tt0472062/

The US also backed and supported the ISIS-affiliated 'rebels' in Syria. This is a fact. The US soldiers stationed there were not fighting on the side of Assad. I served in the US military, and I know for a fact that we assisted various Islamist militias. Fellow soldiers were torn about this, knowing full well that we were backing and arming people who were religious fanatics.

Your characterization of the 'anti-Israel groups' in the US as Marxist is misinformed. Clearly you have not interacted with many of these protestors or know much about leftist politics in the US. If you did, you'd discover that most are 'liberals' or 'progressive' types that are not Marxist and embrace Capitalism - they just want a 'kinder, gentler' version of it. In fact, actual Marxist and various Trotskyist groups frequently clash with them, and they regard each other as ideological opponents.

Whatever your opinions are regarding Marxist or Marxist-adjacent theory, one thing cannot be denied: The polarization of classes has never been greater than it is now in the USA (and around the world). If you can't understand how the Oligarchs and billionaires that truly rule have interests that are diametrically opposed to the rest of society or those whose labor they enrich themselves on, then I don't know what to tell you. The rich are getting richer while the poorer are getting poorer, just as Marx predicted. Fact.