I was curious about this from a trademark angle (it seems against the spirit of the law if not the letter) and apparently it's generally permitted to show ads based on a brand keyword as long as the ad itself does not contain any trademarked terms or images. I don't personally agree with that but it supposedly been tested in a few courts.

It's common practice in Google Adwords to book your competitors' keywords.

It's also common to book political ads in newspapers that will be placed next to articles discussing that topic.

Whoever pays most, gets that screen/paper space.

Yes, Facebook is likely violating trademarks. Its quite disgusting to see a $500 billion dollar company fighting a non profit with such ugly tactics.

New-old word: brand confusion