I think the rule was created because underwater racing is not that interesting to watch for spectators and more difficult to officiate from the surface. Maybe all we need is a bunch of GoPros stuck around the pool and we can see a new race category?
A swim coach told me that in 1950s people used to do the first lap of breaststroke underwater but people kept passing out. It wasn't safe for youth sports.
The real reason is safety. People have known about the efficiency of swimming under water for the longest time, but competitors would pass out or even die when they held their breath too long. So the rules changed to force people to the surface.
There is a sport called finswimming which has underwater speed disciplines (apnea or with bottles). But as the name implies it comes with the use of fins.
Additionally consider (as was pointed by
swarnie in https://news.ycombinator.com/item?id=44542285 ) that there exist clothing restrictions in Olympic swimming - in my opinion this is also a contradiction to the spirit of "freestyle".
The usual argument against clothing restrictions (see also supershoes in running and various aero stuff in cycling) is that you want the sport to reward the best athletes rather than turning into a technological arms race. This is especially complicated in sports where people don't get to choose their own gear and so (for instance), whether you have access to the best shoes depends on who your sponsor is. Back when Nike was first rolling out the first supershoes, you would sometimes see athletes sponsored by other brands actually wear Nikes with the logo blacked out, because it was just such a big advantage.
As another comparison point, look at Formula 1, where technology is a huge part of the competition, with the result that a driver can be dominant one year and then fall way back the next because of some technological shift. Of course, even F1 does tinker with the rules a lot to try to preserve competition, as when they banned electronic stabilization.
F1 is a weird one. Technology can make a massive difference. I remember the 1970s when a car with a skirt destroyed the opposition by sticking to the ground and the six wheeled beasties and the other wacky stuff.
Sponsored by fags (obviously)
F1 is all about the drivers except it is also all about the marques (who pay quite a lot for it and need to show a return).
The rule book for F1 is pretty daunting these days and I'm not too sure how much is driver and how much is car these days. I do know that F1 drivers do abuse themselves badly during a race - they experience G forces that would make you and I weep and probably pass out.
> there exist clothing restrictions in Olympic swimming
My argument against this is that there are already so many activities where less wealthy are priced out. Most prospective athletes (or families) don't have a bunch of money to shell out for stuff like hydrophobic full-body suits, or hockey gear, or whatever.
