Overall, my view is no drinking and diving. I've never had a drink before a dive or during a surface interval. I pretty much stick with water when I'm doing any sort of multiple-day dive scenario.
However, and for me, this is a big however; I go along with Catherine on the overdoing of 'zero tolerance' about just about everything these days. Do I think having a beer during a surface interval is a good idea; for me, no. But I'm not everyone.
Clearly, I can't think of a situation where alcohol would benefit a diver. There is no good reason to drink before a dive in my opinion. But adults should make their own decisions.
Would I dive with someone who had a beer prior to fins in? I'm not sure, it would depend on a lot of variables. I dive with people who are on medication; who may not have had enough sleep; who may be in the throes of emotional turmoil, all of which may affect their diving and decision making. I evaluate each of those situations and then make my decision.
As a DiveCon, I would absolutely NOT allow anyone who had been drinking to dive in any party I was leading. If I were involved with a dive boat, same thing; if for no other reason, the liablilty issues. I believe that was the genesis of this thread, so it is worth addressing.
Jeff