It goes beyond that though. The left sympathizes with Islam because they share a deep-seeded animosity and hatred for the West, particularly America. Leftists are by nature hypocrites capable of juggling multiple thoughts or opinions that are completely contradictory in every way--and they do this in complete harmony. The proclaim hatred for Christianity and claim that religion is an antiquated concept that promulgates the white male patriarchy--or whatever the hell it is they believe--while embracing a religion that is contemptible in their treatment to gays, atheists, women, Jews--basically anyone that disagrees with them.
Leftists have been fed this steady diet of bullshit so long, they truly do not see a difference between Christianity and Islam. Unfortunately for them, the rest of America don't have their heads completely up their gender studies professor's ass.