The basic explanation is that Leftists are scared s**tless of Islam, so they bag on Israel as a way to curry favor with the muslims (hoping the crocodile will eat them last).
It’s like Islam is a big bully standing there threatening Israel on the playground, while the Left stands behind Islam saying, “Yeah get him! I got your back! Yeah, we’re gonna mess him up!”
The Left only attacks easy targets that won’t fight back, because Leftists are cowards. That’s why they will mock Christianity relentlessly but are terrified to speak out against the abuse of women or any other negative aspect of Islam.
The Left knows that Christians are good people and won’t murder them in the street, but muslims are not so restrained - so the cowardly Lefties keep their lips buttoned when it comes to Islam!
But what are so many Jews leftist/commies?
You are leaving out something more basic. To get power, the Left needs votes. The number of Muslims in this country is increasing, while the number of Jews is not. In fact, its quite possible that the number of Muslims in the US is greater than the number of Jews already. In any case, this will certainly be a signficantly greater number of US Muslims (compared to US Jews) in 10-20 years. They are just betting on the demographic reality.
Eventually, they the Left will throw gays over the side too in order to curry favor with the more numerous Muslims. Its just that the primary object of Muslim rage is Israel right now.