I've heard hydraulic disc brakes give the best braking control w/o hardly any lock ups ever when used properly. Dunno about riding fixed on trails, sounds kind of ill fitting but whatever floats yer boat.

Back on topic though, try mentioning to said friend that you're doing trail maintanence some weekend and invite him along. It may open the door to explaining the whole deal about erosion and skidding and all that.

And btw, horseback riding causes a heck of a lot more erosion than a couple of skidding cyclists.

Peace.

Hydros give really good modulation, but so does any propery adjusted braking system. They are super-easy to adjust though.

Good idea about using TM as a way to understand the ramifications of actions. Especially if it's a group trail maintenance effort, where there will be a lot of responsible cyclists there. Having authority figures other than yourself often helps back up an questioned opinion. Contact your regional IMBA chapter for TM events near you.