That's not paying for other people's alcohol consumption. It's paying a fair share of the expenses that were involved to create this particular communal experience. Which also means that if somebody is budget constrained, the group may want to keep that in mind - no matter what they order. I've been routinely in groups where somebody with budget constraint paid less. Not because they ate or drink less. But because the group decided that it was their fair share, based on the group's perception of fairness.
