I agree with both of you. My feeling is that things can happen too fast on the trails with unwanted results, without anything to dampen reaction time. I might be a 'lightweight' when it comes to drinking, but I feel that any impairment is too much on the trails, or roads for that matter.
My feeling is that someone drinking on the trails does not only affect them, it also affects me. Either by jeopardizing my safety, or, God forbid, by ruining my trip by having to deal with the consequences after the fact.
JMO.