Yes, there could be very bad books. These books are full of bad ideas and should not be taken seriously. However, placing a complete ban on such items only makes it that much more likely to ban the good items as well.
We embrace freedom because it allows us to self-filter. If we have potentially all the information at our disposal, we can make the best decision possible. The theory behind preventing book bans is that restricting access to information only makes us more dependent on our censors and weaker as a society.
Please read Doug Newman’s article on SOPA (Stop online piracy act) and how this piece of legislation is congress’s attempt at a virtual book ban on the internet.
And, if you love your freedom, tell congress that this is a horrible idea. Don’t be fooled by the name, this is an all out assault on the free flow of information. This law is exactly the thing a dictatorship would use to “protect” its people from “bad” information.