Here's the thing: People can't really prove or disprove this - it is very much a matter of opinion or preference on the part of the owner.

Yes: unsupervised tossing a live rodent or one too large in with your snake injuries and accidents have happened, however - with knowledge of appropriate prey size, pre-feeding and hydrating the rat or mouse, supervising the 'dinner hour' (or minute in some cases) a lot of those 'accidents' can be avoided.

Yes: some captive animals may seem to have a weakened feeding response, which may cause them to not kill their prey quickly and a bite could occur...

However: Snakes eat live prey in the wild - they're hungry when they strike the prey, they kill it, they eat it - and they survive through it all the time...

There are also just the plain irresponsible pet owners out there where these incidents become more cases of 'neglect' - it's the same principal with how snakes end up becoming rescues with burns from heat elements that shouldn't have been used or were unregulated... Does it mean we shouldn't use heating equipment appropriately and responsibly? Definately not.

I don't feed live because it is very difficult in my area to find appropriately sized feeders live, and I don't have enough snakes for breeding my own to be effective. I have a great supplier of frozen rats, and Kitty doesn't seem to mind at all that they are already dead. Even so, if I'm in a pet store and they happen to have a live rat of an appropriate size, she'd get one as a 'treat' - and at feeding time I would be standing close by with the lid off her tub until the rat was dead, but it hasn't happened yet!