the FA movement is tricky for me. I absolutely think everyone has the right to be comfortable and feel beautiful in their bodies, whatever that body looks like. I also think that people should do what they can to be healthy.... so FA gets complicated because it specifically glorifies unhealthy bodies (in that being obese is less healthy than not being obese). To me, FA is no different from pro-ana "thinspiration" when it crosses that line into advocation of an unhealthy lifestyle. YMMV.
I prefer "Body Positive" to "Fat Acceptance"...everyone has things about their bodies they don't like. Everyone. That beautiful woman at the coffee shop, the one you would kill to look like? She hates her (insert perfectly normal body part). We could all be more positive about the way we view and care for our bodies, be they thin, fat, short, or tall.
I say good-on those women for feeling comfortable and looking beautiful in their chosen swimwear. Even if they have unhealthy bodies, that has zero bearing on whether or not they should feel adorable and enjoy the beach.