I think many folks forget that there are some pistols that are totally unfit for rabbits and then some, a few that are really as powerful as the rifle loads some use for deer. For instance a 45 caliber CVA Lincoln Derringer vs a repro Harper's Ferry, or Springfield pistol.
Some of the modern unmentionable muzzle loading pistols have some incredible power (White Hawk eye, TC Scout pistol, Traditions Buckhunter pistol) Frankly there is no reason why a side lock can't be constructed for equal power and range.
I do agree that too many hunters will be out there who couldn't reliably hit a paper plate at 25 yards. But there are too many guys out there who can't hit a paper plate at 50 yds with a scoped rifle. I fear that the occasional muzzleloader hunter will buy what ever is cheap and blunder into the woods. (As too many do now)
With a 10 pound trigger and 9 inch barrel, so many of those cheaper guns are terrible prospects for the sunny day hunters.
A side lock gun constructed for big game hunting should not be prohibited from being in the woods.