Art, as MT Gunny has pointed out, there is no caliber or rifle weight restriction in MT for general big game season. The only restrictions placed on the weapon you use regulate ammunition and are pretty vague, stating mainly that the rounds must be expanding and can not be explosive or poisonous. I believe the incident you are referring to, if it is the one I remember, occurred in Wyoming and didn't involve .50s, but rather custom target rifles chambered for some .338 wildcats.
There will always be simple, narrow-minded fools who try to enforce their own views of what constitutes ethical hunting, and will attempt to extrapolate their own limitations on others. It never ceases to amaze me how quickly people will challenge the quality of hunter and the quality of human someone is when they violate some personal arbitrary range limitation or use a caliber they seem to feel is too anemic or excessive.
I am not one of those people and I absolutely feel like if you have the cash to buy the rifle and the optics, and to develop a load and practice with it, and if you are willing to then pack all this equipment into the field, pick your shots, and hike over to the next mountain or whatever to tag and retrieve your kill, then more power to ya.