I'm not following. If PED's are not against the rules, then taking them would not be cheating, would it?
I think the health risk argument holds more water, myself. It is not realistic to allow PEDs in any amount that the athlete wants to take, because the health risks are enormous. So they have to be regulated on those grounds, which means banning them or introducing limits as to how much is allowed.
If cheating is the issue, then introducing thresholds doesn't make the problem worse. It simply shifts the parameters. So for substance X, where before you have noncheating athlete = 0mg/dl and cheating = 2 mg/dl, under the revised paradigm you have noncheating = 2mg/dl and cheating = 4mg/dl. Of course, it becomes much more difficult for an athlete to know whether they are cheating or not (is it 2 or 3 pills?) But by moving the thresholds, we also move the concentration of substance X closer to the point where the athletes health becomes damaged, which maybe starts at 3.5mg/dl (the liver and kidneys can't process substance X fast enough).
Swimming Workout of the Day: Favourite Swim Sets: 2020 National Masters Champion - M50-54 - 50m Butterfly