I appreciated this post Michael, it really got me thinking.
But I think one thing that affects this discussion is par 3s are really either 3s or 3.5s. There are not really any 2.5 holes. Even a hole that's 100 yards is still going to average pretty close to 3.
There are par 2.5 holes, but you won't find them at St Andrews. You'll find them
in the Meadows in Edinburgh though. That they do not exist on "legitimate" courses, I think, lends itself to my previous theory:
I think there are generally two golf swings in golf: a swing for distance, and a swing for a target.
I am again not committed to this theory, but the lack of par 2.5s lends itself to the idea that people want to take full shots. If we like that premise, then it stands to reason that people like to take the biggest shot they have in the bag by default. Maybe there is an argument for legitimizing the 2.5 on a full course, but I doubt anyone would buy into that, and if they wouldn't I think it says something about the game itself, and the built in assumptions we have about how it should be.