And then there is the opinion of the holy Cure of Ars that even babies should not remain undressed for very long even when they are alone with their mothers because their nakedness would offend their guardian angels. So perhaps even a sex-segregated beach would offend the guardian angels of those who would go there.
In the world, there has been a persistent heresy that the human body (and all that pertains to it, such as eating, sex, etc.) is evil, and/or that the "devil god" created the material world, and the "good god" made the spiritual world.
Manichaeism, Puritanism, Calvinism, Jansenism, Catholic "Jansenism Lite", Jansenist infection, or Jansenist tendencies (the Cure of Ars goes into one of these latter categories).
Just like someday people will look back and see a tad bit of Liberalism in today's Saints, because it was in the air we breathe, likewise we can look back in hindsight and see such infection in the Cure of Ars.
There is nothing "dirty" about the human body! Why would a naked baby offend a pure spirit (such as a Guardian Angel) or anyone else for that matter? Unless the human body were somehow dirty or evil. It's not!
I assure you that ANGELS are not offended by anything that doesn't offend God Himself: namely, sin. And God Himself created the human body.Angels are offended by any sɛҳuąƖ sins, including exhibitionism, but they don't leave the room (or strongly want to) when a married couple have sex in a private setting!
The Cure of Ars did speak about it being a mortal sin to sleep with a child over 5 years old, but that was also because it was assumed that the married couple would be having sex in that bed, and the 5 year old wouldn't be oblivious -- he would be self-aware enough to remember it, think about it later, etc. A 5 year old is no longer a baby.
As for being naked in front of the same sex, it really comes down to modesty. I don't like parading around in front of a group of men OR men/women. I hated having to strip naked in the locker room every day in (public) middle school. It was my natural sense of modesty throwing a fit. And it should have! Our bodies are temples of the Holy Ghost; they deserve covering.
What is one of the punishments given to prisoners, especially in situations of torture? They get stripped naked. Doing this strips them of all their dignity.
Note that at Traditional seminaries, such as those run by the SSPX, the Rule states that men are to be modestly covered in the hallways, on the way to shower, etc. I quote: "A seminary is not a barracks". If there were no issue with men seeing other men without shirts, or even naked, why would the SSPX have this rule for its seminaries?