Easier to sell ads if users don't have to deal with differing opinions. Arguments are hard to avoid and disrupt the casual consumption experience.

Conservative voters probably represent a much smaller portion of facebook's user base than liberal voters, given facebook's age demographics.

There is definitely an assymetry in what kind of hard-line political pages are likely to get banned. They have relaxed a bit in the last few months, but many political pages constantly have to worry about "getting zucced".

I imagine that plenty of people 'report' people after disagreeing with them politically.

Zuckerburg has political ambitions, a little help from the Facebook moderation team might earn him a few favors. He certainly wants that infrastructure in place once he runs.