Some years back, there were long discussions on these boards about whether is was POSSIBLE to have decompression illness while obeying all deco limits on your dive computer. Obviously, it happens to some divers. Other divers violate the guidelines and do not have DCI. Personnaly, I stay well within the decompression limits. Will flying without waiting 18 hours always result in DCI. Almost certainly not. But if you get DCI and it is severe, you could disrupt the flight with adverse consequences to many other people. It is a bit like driving drunk, you might get away with it. But if something goes wrong other people pay the price.