On the beach, it's a case of anything goes. It doesn't matter which shape you are, it's acceptable to dress, or undress, as you wish. Topless sunbathing is common and there are ample nudist beaches in the area. However, lying on a beach almost naked demonstrates how defining a setting can be; it's acceptable. Place a woman in a cabaret show, scantily dressed, and it becomes sexual; people will pay to see her. If she lies on a beach, she'll be left untroubled. Further, a man with a large stomach will let it all hang out on the beach, but will soberly cover it for work. Location matters.
There's a certain anonymity on the beach. One lump of flesh looks very like another and, on a crowded beach, no one is an individual. People can lose their inhibitions and feel comfortable soaking up the sun en-masse. However, once they leave the beach, they stand out as a person and are noticed, not always admiringly.
The social norm changes when a person steps off the sand. There are some people who don't hesitate to walk along a promenade in their swimwear. Men, in particular, flaunt their distended stomachs as they stroll to the cafés, and women in bikinis expose their bodies. And that, I think, is where the line is crossed and their dress sense, or lack of it, becomes unacceptable.
Some areas now prohibit wearing swimwear off the beach. Barcelona has introduced a law and fines people who are inappropriately dressed if they walk along the promenade. Majorca has done likewise. Spain is a liberal country but recognises that a dress code helps to raise the good reputation of an area. Think of Benidorm and the image, right or wrong, is still of loud Brits with exposed beer-bellies boozing in the local bars.
There are diverse opinions as to what should be permitted. I don’t think that swimsuits should be worn away from the beach and the thought of a semi-naked, sweaty body sitting near me in a café is repulsive; but anything is fine on the beach. There’s no logical reason why I think that. Mention the promenade of, say, Miami and you think of sun-bronzed bodies strutting their stuff and wanting to be noticed, but that's not so close to home. There are cultural differences and it depends upon what’s socially acceptable in various countries.
Just my thoughts, but nothing to sweat about, and I'm sure you'll have an opinion!