Why does it seem that some people these days want to treat male shirtlessness as if it is somehow dirty? Of course, most wouldn't say it so bluntly, but if you asked why guys can't take their shirts off at the gym, for instance, you might get an answer like, "This is a family-friendly establishment", or "It's a modesty (or decency) thing". The implication, of course, is that a shirtless man would have been indecent, immodest, and inappropriate for families with small children. Strangely enough, most of the same people might not have had an objection to a bare chested man at the beach or pool, but might have qualms about the same man in a gym or other establishment. While again, I am not trying to establish that men should go shirtless anywhere and everywhere, there is no reason for a shirtless man to be considered indecent, particularly in places where it has often been customary for men to go shirtless and where there is good reason for it (comfort while working out, for instance).
Shirtless freedom isn't about men vainly showing off their bodies, and it's not about sexual innuendo. Rather, it's a matter of comfort and simple innocence. Think of a group of boys playing shirts versus skins. They aren't being lewd, in fact, they probably haven't given much thought to the idea of being seen shirtless. They just aren't concerned with such things. Most guys tend to want to be on the skins side, simply for the comfort of being shirtless.
As a last example, I am going to reference the classic TV program from the 50s, a veritable symbol of decency and innocence, Leave it to Beaver. Here we have Beaver and Wally getting ready to play ball.
And here getting ready to go snorkeling.
Wally reading a book on the lawn, enjoying the sun on his shirtless back.
And Wally working out shirtless.
Just normal innocent boys, comfortable and free. Why don't we all learn to enjoy this innocence?