Part of women’s lib was freedom from restrictive decency laws.
It makes sense when you see what bathing suits used to look like.
And the fact that police would enforce bathing suit rules at public beaches
Star Trek was released in the 60s when the bikini and the miniskirt were very popular and countercultural, so modest clothes would have seemed anachronistic (well, not futuristic).
The 2a is so that the government can press you (and the weapon you bought) into service.
The clearest examples of this is when the government pressed citizens (and their weapons) into service to shoot tax protestors during Shay’s Rebellion and The Whiskey Rebellion.
The government didn’t want a standing army hanging around thinking about coups and figured they could min-max their way around it with militias.
The closest modern analog is The National Guard. A 2a written today with the original intent would allow The National Guard to keep a rifle at home. And there would be no standing army.
“Whatever’s normal.”