Actually he does (Bill talks about so much shit on his show its hard to catologue it all).
The article is a fact check of both Maher and Aslan on the issue of female genital mutilation in Africe. Maher suggested it was an Islamic problem, while Aslan suggested it was a Central African problem. Politifact finds that basically Aslan is right. Female genital mutilation is basically centered in Central Africa, in both Christian and Islamic countries, but apparently the Muslims there support the practice (which is where Maher got the idea from). So if evidence were brought to Maher that Christians from America were encouraging people in Africa to cut on women's privates, I imagine he would be pretty upset about it, and would criticize the Christians doing it (I didn't know that was a thing until you brought it up). Maher criticizes Christians all the time. He does the same for Muslims. Just because he's wrong sometimes doesn't make him a bigot.