I have no issue with people using whatever they want to take an animal so long as the animal is dropped quickly.
First, for those who think they can make a 500 meter shot, I't probably been 10-20 yeas since you've seen the Marine Corps, so you need to actually do some target practice at the range to see if you can still make a clean shot at that distance. And holding a 1 inch group with a scoped rifle at 100 meters does not count.
Second, any animal will drop with a .22 lr to the brain, but will it penetrate deep enough into the chest? Will it cause enough damage? Or, will that bullet just break the animals shoulder blade because you tried to take it with a 500 meter shot with a 30-30?
I'm not advocating any specific caliber here, because I tend to stick with what has worked in the past. I'm not saying I wouldn't get my sights on an elk at 500 meters with a Remington 700 / .308, but by the time I felt it was ready to start the squeeze (probably 10 minutes later) the darn thing would probably be gone. What I am saying is to actually check your skills on a regular basis and that there is rarely suck a thing as overkill.