The reason is simple. "Tolerance" for the secular left means hating the Gospel and the Torah, since by definition Christians and pious Jews (as opposed to the kind who run Hollywood) are 'intolerant' because they think people should restrain their natural lusts.
Muslims are far away, anti-Christian and anti-Jewish, and therefore are allies. The fact that close up and in power, they would even more rigorously regulate such things as sodomy, women's dress, and the like, doesn't seem to have occured to the left.
The spectacle of self-proclaimed 'progressives' lending support to people who want to spread a copy of 7th century Arabia over the entire globe is truly a wonder to behold.
"Show me just what Mohammed brought that was new, and there you will find things only evil and inhuman, such as his command to spread by the sword the faith he preached." -Manuel II Paleologus
The liberals just don't think that the Islamists mean what they say. They think they are simply opposed to "imperialism," like Ho Chi Minh and his merry men. To them the religious rhetoric is not to be taken seriously.