I think it would also depend upon the owner(s) situation. Ideally it would be best if all captive rasied snakes could eat F/T their entire lives, but sometimes that is not possible. For example, out where we live we don't have a ready, reliable source to purchase F/T for the number of critters we have and at a reasonable price. Yes, we could order through the web and have them shipped, but that can be expensive if you only need a small amount for one or two snakes.
We breed our own mice and work with another snake owner who orders shipments so that I can have a ready supply of both frozen and live mice for all of my snakes. Regardless of age, about 90% of our snakes will take either and any live prey larger then a fuzzy is fed with supervision or is killed/stunned before being offered to the snake. We do have a few that prefer one or the other and sometimes it's frustrating knowing they might have to skip a meal if for any reason we don't have the right kind on hand.
So, like Meg said, the best thing to do would be to discourage them, but if they are determined or have limited means of procuring F/T, then strongly advise them to supervise all feedings. For us, I don't walk away from a snake that has been given live prey. I stay until I know the snake has subdued the mouse and keep close watch in case the snake does get bit. Typically the more severe wounds and damage a snake will get from a mouse or rat happens because the rodent was left with the snake unattended for long hours. That's not 100% true in all cases but in many of them it is.
ANYway, I've rambled enough.
Jenn *sinking back into the safety of the shadows.*