The best theory I have is to build rock-solid boundaries, but to do so at a meaningful distance. Humans and animals are good at working with a "duality" of personalities. Children should have plenty of space to explore, be creative, and develop relationships, but going beyond a certain well-established limit brings out the bad cop. A lot of 123 methods looks like, to me, ways to make the kid recognize and respect the bad cop... but still have confidence that bad cop won't show up if they will stay inside of defined bounds.
Constant behavior correction is terrible, and leads to psychological problems. Too much of what I see takes this problem and turns it around to "no correction". That's probably not AS bad for the child, but is inviting disaster on the part of the parents.