"I was guided by the horror stories I read and a few group rides which were squirrely and dangerous... "
Group rides are a different beast. They're probably one of the most dangerous things we do on a bike. The horror stories about single riders or a very small group are just that...stories. The only exception to this is if they are on their aero bars while following. That's easy to remedy, you just ask them to not ride on them. And I agree with the post above about 25mph drafting. Anyone who can hold a wheel in a small group of 5 or fewer riders over more than a handful of miles is probably not going to be an issue at all. Sharing the road with large vehicles is a much much bigger safety issue. I'd still like to hear about anyone who's actually had something bad happen to them while they were pulling that was caused by the person sitting in that resulted in broken gear or a crash.