Education is probabbly the best route, don't tell them you're there to dissuade them, just show them what it can and what it can't do ;)

I've only been in a few situations where "Oh man this is a terrible idea." and education works.... sometimes even if to direct all that energy into something more benign. Sometimes "Ok now they're going to waste a bunch of energy on X ... but at least X isn't going to hurt Y." is a win ;)