That is an important point: if we don't patronize the bar, then the venue will disappear.
Most non-studio dance venues are organized by a teacher or promoter having approached the owner/manager of a bar or restaurant that has a dance floor and the arrangements with whom (or selling point to whom) includes the extra business that a dance night would bring in. If the owner doesn't see that extra business, then he won't have any motivation to allow that venue to continue and not be replaced by something more lucrative.
A local restaurant with a bar has dancing every night, each venue having been organized as described above. I've seen a West Coast Swing night start up there and then get cancelled within a few months because the Westies weren't patronizing the bar -- that night is now Country with lots of beers being sold. Just recently they discontinued our Lindy venue which had run there successfully for about 5 years, because they could make more money at the bar by opening an additional night for the local Mexican work force.
That said, patronizing the bar doesn't mean you have to consume alcohol. They also serve soft drinks and bottled water and I'm pretty sure that their profit margin on those options is a lot higher that their profit margin on alcohol. And again, once you're legal, if you really want to drink then one alcoholic drink to start off with followed by water is a fairly prudent approach to take.
As for myself, I almost never drink when I'm out dancing (which is all partner dancing). From the start, I knew that I needed all my wits about me to survive on the floor, so I simply never drank (besides which the previous 25+ years of being a family man had precluded drinking). And the few times that I have drunk, it would be just one that I'd consume over a long period of time (AKA "nursing the drink"). The one time that I finished a drink before doing any dancing, I don't think it actually impaired me (did not receive any outside observations besides the usual expression of regret at having to rotate to the next guy), but I still felt far less competent and hence uncomfortable about my condition.
OTOH, I've considered that should I ever again be called upon to try to fake free-style, then a drink or two beforehand should prove beneficial. If for no other purpose than to dull the pain.