If you switch seats in a boat, car, tank, the vehicle stops moving. If you switch seats in a helo, well, for starters it wouldn't be possible, and if you switched seats, who is flying the helo? I would rather be in a car sitting there compared to in a helo falling.Can't believe everyone is whining such about it, what the hell is wrong with it? switching seats in cars, boats, tanks etc. don't make people whine.... so my vote is definately No.
Having said that, if the makers of BF2 gave you the opportunity to do that, why not? I would have personally only allowed switching if it was on the ground, if you are with a bot, or even possibly with a person of a lower rank. After all, they don't give much in the way of advantages to people of higher rank (besides unlocks, commander, and of course experience).