I've followed Bill Maher's career off and on since his "Politically Incorrect" days, and I've always noticed his humor is rooted in what he truly believes, and yes, sometimes as with his "we're the cowards" comment that pulled the plug on that show, his sincerity can take him perilously close to offending most people while pleasing only a few.  But to his credit, he's seldom been reluctant to make a liberal guest the butt of a joke if the opportunity presents itself. 

But I strongly disagree about him revealing racist proclivities if what you're referring to is his recent "house servant" remark.  If you actually listen to it in the context of the banter when he said it, it's obvious it was meant as a self-effacing remark, and frankly, I'm almost astounded there are people who considered it a racial slur against black Americans.  I'll concede Bill Maher did commit a serious error that night; he forgot that only in rare circumstances can a white man don a black stereotype even in jest.