From what I've read, the logic behind the FAA limiting a Sport Pilot to one passenger in a C172 is training difference between PPL and Sport Pilot. If that is correct, then why shouldn't a PPL transitioning to Sport Pilot be allowed to carry three passengers, assuming the plane qualifies as LSA (or whatever the new name will be)? After all, transitioning to Sport Pilot doesn't cause a private pilot to forget that additional training. Not looking to debate, just questioning the logic of this aspect of the rule.