What should we call your proposed coalition - dhimmis anonymous? Leftists do actually have a religion of sorts, though I suppose the correct term would be an anti-religion. Leftists are never going to get it. The underlying reason is that they seek the same goal that the Muslims do - the complete destruction of the west. The evil oppressor/patriarchy/untermenschen must be destroyed in order for the free and equal supermen/oppressed/übermenschen to emerge and establish utopia. Leftists see Muslims as their great allies amongst the "oppressed other" in the master plan.
Some allies...you can't be a free and equal superman AND a slave of Allah...those lefty fools won't know what hit 'em...