Basically, his argument goes like this: Why would an eternal God decide to have people from the bronze age write down eternal truths that reflect the social morals of that particular time period in history?
First of all, Bill Maher's comments are very patronizing toward the ancients which is a common assumption I hear many agnostists/atheists mention time and time again. The implication is that since the ancients were so below us, we are the superior ones, since we live in the post-modern age. I beg to differ that our post-modern world gives us reason to boast. Didn't the enlightenment bring us Hiroshima and the Holocaust? And this is the time period that Bill Maher believes the bible should have been written?
Second of all, I don't think Bill Maher understands the meaning of biblical authority. The bible isn't primarily a book about timeless truths as if it is a dictionary or encyclopedia to answer our questions. Like it or not, the bible is an amazingly coherent grand narrative which is rooted in different periods of ancient history. The bible is authoritative when we seek to understand the historical and religious context in which it was written and open ourselves to how God is speaking to us in our present context based on these ancient texts.
Of course, when we look at the interpretation of scripture from this perspective, that means we need to faithfully study the historical time period of when it was written, see how it fits in with the grand narrative, and prayerfully seek how this ancient writing speaks to us today.
I'm not sure if Bill Maher has simply chosen to not go to all that effort or if he's just really that closed minded about religion in general.
Having said all of this, I do think he makes some good points and is a great comedian.