G'day
No matter whether the quads have roll over protection or not it will stop idiots from being idiots, never ceases to amaze me how the actions of a few blockheads can ruin things for everyone else, I agree that quads can be lethal even in responsible hands as accidents do happen but seriously if you try to make any piece of machinery do something that its not designed for there is a fair chance it will bite you.
Being in the small engine industry for many years I have seen horrific injuries people have received from chainsaws, mowers, snippers, leaf shredders and even hand operated garden shears, but all of these items are still on the shelves of hardware stores to this day and many have remained unchanged and still require no training to be able to buy and operate.
Motor bikes are just as dangerous in the bush as quads are and any lapse in concentration can result in an injury, being a fool and driving around stupidly just massively increases the chance of a mishap, maybe its time the humans are fitted with a governor instead of the bike.
cheers
stayyerAU