I don't care what the reasoning is, if I am in traffic, I ALWAYS cover my brakes. It only takes a split second for something to happen, I would rather have as fast of a reaction time as possible. I do agree that to new riders this could be dangerous as they may not be familiar with panic stops on a bike and may lock up the front. For this reason I try to do braking drills myself just to keep my skills pollished. If you practice it, then it will become second nature and you do not have to think about it.
Another thing, I always use my rear brake. No many of you will say, but if you are not careful you will lock it up, putting you at greater risk of having a highside. To which I respond, if you keep your skills sharp that risk is minimized as is your stopping distance. Now the Ex500 is not a stoppie machine so the arguement that the rear brake is useless when the rear tire is lifted in the air does not apply as it may on 600's or 1000's. Yea a novice may lock his brake up while learning to use it, which may cause him to highside or fall, which is all the more reason to do drills in a controlled enviroment and practice practice practice. To me this argument is no different then someone saying they will only drive an automatic car because they might stall the car, or even worse stall it at a light infront of everyone. Sure if you are new you may screw up, but this is why you work to improve those skills.