Take Trump out of it for a moment, and just look at Bill Maher. I think there's a tremendous amount of value in his show, and how he approaches discourse, because he's one of the few places where you actually can get every side. He will bring on anyone with a unique perspective, agree, disagree, whatever, and that's almost impossible to find anywhere on television anymore. And he's also not afraid to have an imperfect conversation. A lot of commentators don't want to say anything until they know the party line. Bill doesn't wait for that, and he doesn't hew to it if he doesn't agree with it. Sometimes, he says horrible things, or does horrible things, because he doesn't follow any orthodoxy. If his show goes off the air, it will be a huge loss to the culture.
That being said, there are lots of reasons to criticize him, and this recent comment, while it certainly is the clearest example I know of him crossing a real important cultural taboo, in substance I don't think it's even the worst thing he's said on his show.
http://www.huffingtonpost.com/entry/bill-maher-history-bigoted-comments_us_5932bcb5e4b02478cb9beaf6
Now, no one here has defended Maher. Folks just brought him up as if somehow a guy on the putative left can balance out Trump's misdeeds, and just expected that people would defend him, and that would somehow make it a wash. It doesn't. Two wrongs don't make a right, and Bill Maher is a guy with a TV show. Donald Trump wields real political power, and has the support of a real political coalition.