We are on vacation right now and my SO actually wears only the bottom of the bikini and goes bra less to the beach, because she says it's unfair I can free my nipples and she can not. Well that's pretty fair I would say?
We are European though and probably a bit less prude than US Americans.

Swimming apparel is explicitly made from slightly thicker and very different material, keeping you from looking like you entered a wet-tshirt-contest. That alone is a big subconscious help. Or are you talking about the amount (or rather lack) of clothing?

People here saying consent (fair enough) but let me tell you, clothes are suggestive. There is more to suggestion and context than the actual content. Is anybody shocked to see a nude statue in a museum or something? Or in a painting? Now how about somebody wearing nothing but a g-string and a harness? You can argue the harnessed person in a gstring is less exposed than any nude. I say no. Clothing adds to the exposure sometimes. Underwear isn't meant to be seen, so when it's seen, it prompts judgement.

People are right in saying it's context and consent, and it's not completely gendered. Men's swimsuits are basically just boxer shorts. Normally I'm not self-conscious about that, but a few months ago I signed up for a toddler swimming class with my son where I wound up being the only Dad, and suddenly I felt a bit exposed. I think the normalcy of walking around in nothing but a small pair of shorts kinda evaporated once I was the only man in the room.

social conditioning

I just got done working a comic convention this weekend. You might be pretty surprised by the general lack of clothing most people wear to those things (calling it a "costume").

Just this weekend alone, I saw at least five guys walking around without a shirt, and I don't know how many women wearing things that showed basically everything. Like so tight and thin I could tell what kind and color underwear they were wearing.

And this was in Indianapolis, far from a beach or lake, right in the middle of downtown.

We have an ad for ice-creams in NZ that covers this topic https://youtu.be/h-Lx2ihpGbc

The same way that pigs are food and dogs are not. Cognitive dissonance.

Something about feeling like a mom I guess? Idk I don’t have kids! xD For me, rocking a bikini = feeling confident about my body. I used to wear smaller bikinis when I was younger but now I find swim shorts much more comfortable, practical, carefree. Why are us women wearing small tight swim clothes anyway, that you gotta adjust, fuss with the strings, prevent the nip slip, etc. Meanwhile men wear comfy shorts? Well it helps that I’m not at that stage in my life where I’m looking to date or impress anyone lol.

I will say that if I were diligent about going to the gym and had a rockin bod, then yes. I’d probably wear that bikini to show off my hard work😉💪🏼

I can’t speak from a women’s perspective, but wearing swimming trunks in public feels very different than wearing boxer shorts in public.

I've never in my life been comfortable with anyone seeing me on a bikini, no matter how good I feel about my body. The "difference" between that and underwear or virtual nudity never permeated my brain 😂

Basically I think it's weird that they're treated so culturally different and don't feel comfortable in them myself, but also support the choice of whatever bathing suits people prefer or nudity in designated areas

Context and culture and expectations. I agree with your point, but there isn't a logical/sensible answer to these things.

I'm a man and I don't think it would be acceptable for me to wear a Speedo swimsuit or have my bum exposed the way some thong bikini bottoms do. Communities, societies and cultures dictate what's acceptable in an unsaid way. It is what it is.

Some commenters in this thread are reacting in a pointed way because questions like yours seem to imply that there should be a judgement of control of what women can/cannot do. People can do what they want, but it's also OK to think about the absurdity of society's rules......like why some women with a certain body shape can wear bikinis but others get disgusted looks. Or why it is so socially unacceptable to wear the Borat mankini. Or taking it further: why is full nudity so unacceptable and offensive? My answer is: there is no logical answer and this is what the societal collective seem to have agreed.

Do what makes you comfortable.

You'll be out with family and friends, in an environment where most any swimsuit would be expected. Any lack of confidence would come from your own internal comfort, so you do you.

As a more practical suggestion if you're on the fence, wear a wrap? Then you can decide how you feel in the moment.

I can't contribute much except that I've asked myself this question many times. I guess some underwear is see-through but other than that it's kind of the same attire.

IMHO it's really all about you being worried about how others react. Speaking as a 50 year old guy, I would walk around naked if it was normal in society. Put the bikini on and stand in front of a mirror. Make sure you're confident that it looks normal (no tags still showing, nothing that is too revealing or pinching in the wrong spot or whatever... then put it on and go out in public and don't think about it. It'll be fine and nobody will think twice about it other than maybe saying "damn she's keeping herself in shape!"

It'll be fine. Don't let others get in your head so much that it determines what you're going to do or wear.

It does feel like going out in underwear, to a place where everyone is in underwear, and the people wearing full clothing look out of place. I don't even have a perfect body but grew up near the beach, saw every possible body type in swimwear. So I am comfortable enough looking near naked in public, since everyone is. It's nice.

Consent. If you see a woman in her swimsuit in public it's because she wants you to. If you see a woman in her underwear in public it's because she wants you to. If you see a woman in either when she DOESN'T want you to then she's likely to have the same reaction. Same as dude's in swim trunks. Public? Fine. Walk in on changing? Likely to be a bit "ahhhh!"

It does tbh

I wouldnt go out with my underwear in the garden.
But going with my bath shorts is totally fair game to my mind.

I would even hesitate dipping into the beach with my underwear even if it was with my mother/father.
It's somehow weird to me. Even if it's totally irrational.

You get used to it, especially when nobody cares. Walking into a corner shop in nothing but shorts is pretty Sus in a city in winter, but if it's a hot summer day and the corner shop is near the beach, it's fine.

Ehm, not the same... but I think that how everybody is dressed affects how we perseive our nakedness. Once i went in a trip to Brazil, and felt a little ridicule by how long my swimming shorts were. I ended up buying a swimsuit there... that I can only wear if i ever go back to Brazil.

I'd say it's the intention.