I've heard all the stories, and done all of the dumb things coming up in the arts from the late fifties. I came originally from a traditional Chinese school where equipment was never used, and the emphasis was on conditioning weapons through training.
In my heavy sparring years, we never wore anything, not even a cup. Putting on shin guards or wearing a mouthpiece was considered soft while I was training and banging with some of the best that ever competed. I watched prominent players loose teeth, testicles, and bend fingers and toes the wrong way.
As I got older, (and presumably wiser) I slowly began to finally protect myself. First came a mouthpiece to protect some very expensive dental work. Than a cup as I saw a competitor who would violate the tournament rules because he didn't believe in cups, loose a testicle. My feet took a beating working out on all those concrete floors and no mats, and my feet became so flat the doctor ordered me into shoes. Not being able to afford time away and scrapping on the job got me into knee pads.
But the kicker was Ed Parker. He said wear everything you need to wear to protect your body for the long term. You have to use it for a long time. Yeah, I heard all the "wise" guys and their neanderthal logic for punishing the crap out of your body, and believed it for awhile myself. "You're not going to be wearing a cup if you get into a fight on the street" was a favorite 'brilliant' observation. Choosing to train for contact and having it happen to occur sometime in your life are quite different.
Let's see now; boxer wear headgear, mouthguards, handwraps and gloves when training contact. Football players wear mouthguards, all the pads, and a helmet when they train contact. Even baseball players put on a cup and helmet for batting practice, and none of us are less manly (except Carol) for protecting ourselves when we know in advance we're going to engage in contact. Having someone possibly kick at your groin perhaps one day in a confrontation, is a long way from an intentional act over and over again, while training to defend yourself.
I tell my students, as much as the training is important to you, staying healthy for making and enjoying a living, longevity with your family, and simply staying as healthy as you can for as long as you can is the most important thing in life. To that end, I let them wear every pad under the sun if they feel they need it, even though I only mandate a mouthguard and a cup (male and female).
They don't feel any less prepared, and telling them to NOT wear protection when they train because they MIGHT get in a fight one day and won't have it, is as totally rediculous as it gets. Conversely, maybe we should start wearing helmets because we might fall down one day. Some things just don't make sense, unfortunately in hindsight. I just want to make sure I don't pass my own stupidity on to my students.