Men do sometimes have boobs, and women tend not to find them attractive (some do ofc) because they are a sign of a poorly maintained body.

If they were a normal feature both sexes had regardless of health, like women sort of do (tho it is still absolutely based on health and hormone levels so this is kinda disingenuous) it would probably be like nice legs or nice butts; one can appreciate nice ones but it wouldn’t be a secondary sex characteristic anymore, so neither sex would be likely to have the present level of obsession with them.

I don’t think women would be particularly concerned with breasts if men had them, too… for one thing even lesbian women don’t tend to get super giddy about breasts now because they are exposed to them a lot more readily and less sexually than men are, so they just aren’t special in any way, even if they are a lesbian’s preferred physical characteristic. This would become true for men as well re:female breasts, but more than that, I can’t really think of any male physical trait that similar numbers of women like the way men like breasts. And I doubt breasts would end up being it for women.

It’s kinda amusing if you think about it but men are absolutely obsessed with genitalia and sex in a way women just aren’t, usually, and that translates to being absolutely obsessed with one’s own penis, such that it -is- a big chunk of the male personality (for the record I’m not saying this disparagingly, I find the differences to be fascinating as a fellow ace, and just listened to a book about erectile dysfunction where this exact tendency is mentioned many time for its usefulness as a diagnostic tool to determine if ED is caused by physical or hormonal issues). And along with that obsession with their own genitalia being the obvious appendage of all their musings, comes a twin obsession with a single highly obvious female body trait, breasts.

Women just don’t operate like that at all. Maybe it’s socializing, maybe it’s inherent, but either way, I don’t think breasts on men for women (or any other trait, frankly) would or even could be like breasts on women for men. I think the problem is that male secondary sex characteristics are basically optional. Men basically get body hair, bad smells, a lump on the throat, and the ability to put on muscle more easily. Other than the Adam’s apple, which isn’t particularly prominent, none of those things are necessarily permanent. You can shave and shower and if you don’t use your muscles they fade, so men don’t have “one major trait”, like breasts, and women are thus more varied about the trait they find most attractive.

For the other questions - women shirtless normal? I mean that’s just a socializing thing. There have been cultures where women are topless just as readily as men and it’s nbd. This is entirely puritanical nonsense.

For breast cancer color - did you know pink used to be a boys color and blue girls? I see no reason the color couldn’t stay pink. But if it was a big deal for both sexes I don’t think it would ever have risen to the sort of prominance it has in society now. Breast cancer as a big deal is because of women making it a big deal because it disproportionately impacts women and men don’t tend to advocate for women’s issues. But if both sexes were impacted it would be more like lung cancer or something, just sort of non-gendered PSAs about your boobs trying to kill you.

Here’s a fun thought experiment in similar spirits.

If complex intelligent life evolved an an encrusted ocean moon (like Europa, which has liquid ocean topped by miles of ice crust, preventing any light or anything from penetrating to the depths), what would their technology look like, and what would their view of the universe be like?