The suggested reason is shallow. One of the most fundamental commitments of the Left, since it got that name from the seating arrangement in the French National Assembly, has been hatred of Christianity. Left-wing islamophilia is an based on the adage "the enemy of my enemy is my friend."
Sometimes a shallow reason is all that is needed. People make trainwrecks of their lives over guilt pretty commonly, usually through the use of debasing substance abuse or other self-destructive behaviours. Granted, there seems to be a growing anti-christian aspect to all this, but ironically, Christianity contains the means to free ones self of guilt for past sins and move forward with a fresh (reborn) life and persona.
Apparently, that just isn't everyone's choice. I would wager a great deal of the animus is striking back at an ill-perceived caricature of Christianity, because that caricature exposes shortcomings which make them feel guilt and anger for feeling that guilt (in a strike at the messenger, not deal with the situation mentality), and not from knowledge of either Jesus or His teachings.
Maybe they just want to blow random people up and cut off heads, too.
