To you, maybe. How about the minimal swimsuits worn by Olympic swimmers and divers? Purely sexual? Of course, some peole wear skimpy swimsuits for sexual purposes. But, most don't.
The majority of French wear tops on the street, so even they acknowledge a sexual component to the bathing suit, since they wouldn’t appear that way at a cafe, no matter how comfortable it might be.
Some clothing is appropriate in certain circumstances, but not others. You can wear jeans to a ball game, but not to the opera. Going topless is appropriate on certain beaches, but not in restaurants. Different societies have different rules, of course.
The existence of a European double-think on the issue of co-ed European beaches doesn’t mean that European women don’t know that a topless woman in public is generally indecent.
It's not doublethink. It's just an understanding that different clothing is appropriate in different circumstances.
I've never found the naked human body indecent, even in certain public contexts.
Functional racing swimsuits are shaped by the demands of hydrodynamics. They minimise the breasts, for instance, and are clearly designed for reasons other than prurience. The increasing tendency of top-flight swimmers is to wear bodysuits covering more and more, not less and less, to benefit from the lower drag of the suit.
Your argument of “appropriateness” precisely begs the question. Even in France, not all beaches are topless or nude, so even the French acknowledge that not all have bought into the toplessness double-think, and it is certainly the case that such exposure was not considered acceptable, say, 75 years ago. All that citing Europe does is note that their moral disintegration is about 50 years further advanced than ours.