On Reddit, majority are Americans. In America, the Christian fundamentalists have considerable political power and a loud voice. There's going to be a stronger reaction against the religious right because they've had a strong impact on society in the past and continue to do so. This part of Christianity is local for a lot of us, so of course we're going to feel more strongly about it. Plus, there's lots of us who were raised in that fundamentalist environment and still harbor some anger over it.

There are aspects of Islam which are just as conservative as the American religious right. Some sects which are even more conservative. However, in the US, Muslims don't have any political power, their voices aren't very loud, and they don't impose their beliefs on non-believers. The places which do impose on others, and have the most virulent forms of Islam, are places where few of us have a voice or vote. All of this lends itself to a "live and let live" attitude on the left.

On top of that, vocal criticism of Islam is often associated with Trump, various racists, people who want an eternal war over there, and right wing politics in general. The criticism of how Islam treats women or gay people frequently comes from critics who take stands against feminism or gay rights in the US. This leads up to people who hold off on criticism because they don't want to be associated with all that noise.

As long as they're white, anyway.

The white ones are usually the ones with the political power and the loudest voices. Conservative Christians of other colors would get the same criticism if they had the same level of influence. There wasn't any shortage of criticism of the very religious and the very non-white Ben Carson when he had his moment in the sun.