You are right, of course that it depends on how you play the guitar as to which hand (fingers actually) is doing the more complicated work.

Unfortunately your comparison with swimming doesn't exactly hold up. Apparently, using your logic of getting lefties to use a righty guitar from the get go, you also might advocate not letting kids doggie-paddle, since they're wasting time when they should be moving directly to the crawl. I would think it's better to let new swimmers and new guitarists feel as comfortable when they're getting their "feet wet." I wonder how many lefties have been discouraged from playing an instrument merely because they never had the option to play one the way they feel is natural.

The only real argument I see for righty guitar playing is that there are more of them out there, so if you don't bring your own to an event you can always borrow someone elses. Oddly enough, I don't share my tin whistles with anyone and I always bring them along if I think there's a chance that I'll get to play. If I can do that, why can guitarists? If fact there's one peorson who used to come to song circles and seemed to generally forget his guitar. He wasn't exactly liked since he was often imposing on other players.