I don't see the left as making "special" accommodations for Islam. In my opinion, and I'm a leftist, it's about equal treatment of all religions. This thread is not set to have any sort real discussion on this, it's set up to bash.
Christianity is the dominant religion here and the dominant religious influence on our culture. That's a given with 70% of Americans identifying with that faith. Islam comprises 0.8%. Given that, we are much more likely to encounter efforts by Christians to assert their religious values on us. We have a raft of "religious freedom" bills attempting to legalize discrimmination based on religious values - Christian religious values. We had a similar raft of legislation banning Sharia in our courts (a perfect example of a solution in search of a problem).
When you say leftists are less tolerant of Christianity than other religions, a big part of that is it effects more than other faiths. Where I DO see issues with the left is when they they attack every thing Christian under the guise of separation of church and state. Who CARES if there is a public manger scene at CHRISTMAS? It's stuff like this that shows up the intolerance of the left.
There is a legal term called "REASONABLE ACCOMMODATION" in regards to religion. This means that an entity should strive to make reasonable attempts to accommodate the religious needs of its people. If a school child wants to quietly pray he should be able to, if he needs time off for a particular holiday, there should be a way of accommodating it. ACLU has supported numerous cases on behalf of religion, and Christianity in particular, supporting these rights.
Where does that leave Islam in the United States? Unlike Christianity, the favored target of the "Regressive Left", we have the "Regressive Right" going after every attempt at REASONABLE ACCOMMODATE as if ANY accommodation is a step too far. If a Muslim woman seeks accommodation to wear a hijab at work, it is labeled Creeping Sharia, if it's a Christian wanting to bring a bible to school, it is religious freedom.
We need to be able to accommodate all of our religions with the same level of respect but regressive on either side oppose that.