Why would I care? Living in a state where it's stinking hot at least 10 months out of the year, guys wearing shirts without sleeves, while not all that common outside of the gym or beach, are also not unheard of. In fact in the more rural, to put it generously, parts of the state, plain white tank tops, aka "wife beaters", are sometimes standard daily fare.
I usually wear a regular sleeved t-shirt when I go out, but also have on a tank top maybe half the time at the gym and when I have to go somewhere else afterwards and can't or don't wish to change. Ditto for the beach or around the house.
The only thing I really think somewhat negatively of is the guys who wear stringer tops in the gym or elsewhere as it is so minimalistic that at that point, why even wear a shirt? And while I don't really need to see their teats hanging out, but it also doesn't rise to the level where it personally bothers me. In fact I just laugh at them inside, especially when the same guys who are trying so hard to impress others with their upper body muscles always wear sweat or long pants to hide their chicken legs.
So while I initially thought the question odd that someone would think a straight man might be offended seeing another man's bare upper arms, but then I remembered this is coming from the same poster who thinks straight men should only watch lesbian porn because images of straight sex would somehow be a turn-off and then it all made sense.