As a fellow fan of 'good clean fun' but as someone who can also tolerate a pint, I totally see your point and think good clean fun is more appropriate for professionally-aligned events.
The thing is, there are levels of drinking. There's having a few beers in a group to get the laughs rolling (which is still reasonably clean fun and many non-drinkers are OK in this environment).. and then there's the raunchy American style "party" drinking (i.e. doing lots of shots, beer pong, getting drunk as fast as possible). Non-drinkers will not fit into that sort of environment at all.
The drinking in the story here sounds more like the latter and IMHO is rarely appropriate, especially at a professionally-aligned event.
(point being: blame the perpetrator, not the substance)
My answer to him is that alcohol often helps folks loosen up. It's great, and fun, but only when you take it in reasonable moderation.
Most startups are founded by 2-3 men who are usually close friends both professionally and personally. This means that they probably have a history of working together, coding together, eating together and drinking together. Since professionalism in our career is based largely on what you consistently deliver and this is directly and unambiguously observable, indirect proxies for professionalism like dressing in a suit and tie or abstaining from alcohol are not paid lip service. It's this very uncommon, but perfectly rational definition of professionalism that makes our career more accessible to people based on their skills and less dependent on their social class, social skills and social network. Yes, those three things matter, but they matter a lot less in tech than in other industries.
With that in mind, we don't automatically put drinking alcohol while producing our work product in the list of things that are taboo and unprofessional. These norms stick with a company as they add on new employees, including eventually women in the case of startups founded by men.
If you've never been on the founding side of the equation, then its easy to be dismissive of these norms within a company when you join as a latecomer. From the perspective of the founders, there is an element of a faustian bargain in growing your company. On one hand you are succeeding, but on the other hand you end up having to forfeit people for processes and forfeit much of your company culture for a small subset of your cultural norms. It starts feeling less like a family and more like a bunch of people who cooperate for their financial well being. It's perfectly natural for those in tech companies early on to lament the loss of many aspects of fun as a company matures.
Just as the founders doing the recruiting need to be sensitive to the needs and expectations of new recruits, people joining later need to be sensitive to the fact that the founders and early employees are giving up things they hold dear to them to accommodate the needs of later hires.