Maher makes his living putting people he disagrees with on the air to make fun of him. I doubt he'd want to silence such people completely through censorship if it meant he couldn't ridicule them.
Bill Maher may be the sort to wish away all guns, but I suspect he's too busy getting high and playing with himself to actually run anything, so that's one thing we don't have to worry about.
Allowing people you disagree with on the air only so you can make fools of them is a form a censorship, especially when your oppositions position is scripted and your response is scripted for laugh effect.