Never let it be said that we don't pick on liberals here. Maher may have said some clever things in his life, even as a political commentator (he runs the HBO show Politically Incorrect), and he has gained notoriety as a critic of religion (for a focus on Maher’s positive contribution, see this). Then again, David Berlinski wrote an excellent introduction to calculus. Being smart, and being right on certain topics, doesn’t guarantee that you are not a loon. Bill Maher is a first-class loon.
For one, he is associated with PETA, which is at least borderline. After all, PETA has decided that fish should now be known as "sea kittens" (to stop global overfishing) and they have sent demands and cash offers to towns requesting that they change their names, including Hamburg, Fishkill and Rodeo. Their alternative for Hamburg was Veggieburg. The suggestion was serious. They also had a campaign against eating meat called “The Holocaust on your Plate".
In any case, Maher is an anti-vaccinationist and a germ theory denialist, which means that he belongs to the looniest of the kooks of there. He has even made the tired but stupendously idiotic (and false) claim that Pasteur recanted germ theory on his deathbed, which is as idiotic as the strangely parallel, idiotic and false claim about Darwin. Predictably, Maher’s anti-vaccinationist rants are the typical straw man and conspiracy theory mongering. To get an idea of the depth of Maher’s ignorance and idiocy, look at the dialogue reported here.
Some severely mentally ill person at whale.to thinks Maher is a Satanist, but then almost everyone else are apparently Satanists according to the site.
Diagnosis: Sorry, Maher is a total moron, and as cranky and anti-science as they come. He may not primarily be known for his anti-science lunacy, but he has enough followers to be worth paying attention to. A potential threat to reason and truth.