> Why shouldn't Facebook take down the ad that's calling for a break up of their Company?

This is surely not the first time someone posted an ad hating facebook, but they do take down all ads that use facebook's name and logos. This makes sense and it's totally normal (and probably automated), though her campaign team probably planned to use the takedown for political gain. By allowing this one, Facebook is doubling down on her game, i would say it is smart move on their part.