my health club is pretty commonly a big sausage fest- large open showers and sauna, steam and hot tubs within the locker rooms themselves. That being said regular club users know after a while who likes to show off, and which members are 'all business.' You get to know which guys go in to allow their cock and balls to be seen, and which ones who would rather have a private stall.
There are some guys that do plently of open looking at the others while they cover their bodies with suds, and they just look each other- full body, then in the eyes and smile. Others will turn to the walls and keep task oriented. Almost all of the guys there will soap their junk in a way that when they turn around to the other guys that they are 'fluffed up'- not hard or semi- but just as a matter of pride to not look like the victim of 'shrinkage' among their fellow dudes.
I like seeing a guy who is naturally hung come in the showers and then one guy will see it and start to bone up a bit, and then all of the sudden 5 or 6 guys are fluffed up. No major deal- there are so many honest factors (outside of sexual interest) that can cause that to happen that when it does no one takes it seriously... seems pretty innocent. Admittedly- an outsider or gym guest walking in on that would probably freak out and might run kicking and screaming- but after a while using the same club at the same time of the day each day, well guys get to know each other and are more comfortable about hanging out together... it happens.
As for the actual 'invasion of privacy part' - if someone comes in who is prudishly covering himself to avoid any peeps whatsoever- that's human nature to cause interest in catching a glimpse at what remains covered. And bottom line, if the guy goes to the team shower and I am interested in his body, I might time it to go and peek once, discretely, at what he was covering up. He can choose to turn away or put on a show, or leave. But if he is a stranger and I can't read his comfort level, I will not press the issue because there are plently other guys who are into the opportunity for male bonding and don't mind you openly looking at them.
So it's not so much for me about peeping indiscriminately as much as knowing the guy's comfort level about showing his body off.