Having your underwear show when one is wearing an open collar, business outfit is inappropriate.
I wouldn't say leaving the top button open on a dress shirt gives a "70s porn look". Three buttons? Sure... but no one wears the uniform like Tony Montana.
I love the Marine uniforms... but having a white underwear t-shirt showing is a fashion faux pas.
In reality, it's simply a problem for y'all with no chest hair who are envious of us who do. 🖕