It's an ad, not organic content posted by users. If the latter were blocked, I could see it as censorship.

Should <insert name of television or radio station> news be required to run ads that are critical of itself?

Users aren't paying Facebook to host their content. FB have zero obligation to continue doing so. They are well within their rights to censor perniciously and arbitrarily.

Yeah, they probably censor child porn, and other things, too. Don't you support censorship?

If Facebook wants to lose it's safe harbor protections, then yes, it has the legal right to censor content.

I doubt that Facebook wants to lose those protections though.