Quoted:
I'm gonna guess it has a lot to do with people who don't respect the rules and think its OK to pop some FMJ at the steel and destroy it.
Or maybe the fact the the guys who generally shoot FMJ are guys who come out with a semi-auto and pop off 300 rounds in 30 minutes doing mag dumps while hitting exactly nothing.
That's a pretty broad brush you're painting with there - not everyone shooting FMJ is "popping off" and doing mag dumps. In my experience, the opposite is true. Mosins, Mausers, Enfields, and yes - even those scary, evil, non-sporting semi-autos. The list of firearms where it makes sense to use FMJ ammunition is pretty extensive and not everyone thinks 20 rounds a day from a bench is the be-all-end-all of the shooting sports.
Using your own example, 300 rounds in 30 minutes works out to a whopping 10 rounds per minute, not exactly in the "spray and pray" category. If that's too fast from a bench, then your average Appleseed qualification round must be a frenzy of terror. If you want a safe range, put rules in place and then watch the damned range - if some jackass is behaving in an unsafe manner or tearing up the steel it should be easy to see. If it's a problem then boot his ass off the range - problem solved.
His range - his rules, but blaming the ammunition for poor range behavior is exactly like blaming the gun for the crime.