I think it's a intellectually dishonest to try draw a parallel between a local store that has a reach of hundreds (maybe thousands), and a platform that reaches and influences the world-changing (or at least country-changing) decisions of over a billion people.

From a strict business perspective, of course you're right: an independent business that offers a subscription product should be allowed to terminate ongoing uses of that product that it doesn't like.

But from a social and political perspective, FB censoring ads like this makes them look very, very bad, and basically proves the point that they have way too much control over what news and information reaches a troublingly-large number of people.