The Left would support Islam because of the attacks on America via the principle of the enemy of my enemy is my friend.
As David Horowitz pointed out the Left arrogantly thinks it will get the remains of what is done with America when the Islamic types get through with it. If -- G-d forbid -- such a thing happens, I think the Islamics --not the Left -- will rule what was once America and those of us that survive will be dhimmized.
....and the lefties, with their love of feminism, atheism, and sexual promiscuity will be the first to be beheaded.