I'm not necessarily against it. a lot of people obviously abuse the fact that it's available on a plane. I'll occassionally have a beer or something, but do people really need like 5 cocktails for a 1-2 hour flight?
I'd say limit to two per person (or for longer flights, one drink per person per hour in the air). if they don't let drunk people get on planes, why should they have an open bar on a plane? kind of ironic don't you think... you can't get on the plane if you're smashed (makes sense since you're more likely to be disruptive and a risk to all involved) but you can get smashed on the plane. just slightly odd