Difference between a performance enhancing drug and a performance enhancing nutritional additive? Between an enhancing pharmaceutical and a medicinal pharmaceutical? Caffeine was not long ago on the IAAF banned list but is now in Lucozade. Phenylephrine and Pseudoephidrine are banned (still, I think) in the US but are in drugs which can be bought over the counter in the UK. Where's the line? And if it keeps changing all the time, how do you police it?
If you can have clean sports, have clean sports. Once a drug is firmly bedded onto the list of banned substances and every test is clean, safe, correct and repeatable, then use of that drug should result in a ban, and I'm happy with a lifetime one. But if the lines keep being redrawn then I wouldn't be happy with a lifetime ban for someone taking a legitimate cold remedy in Estonia and getting banned in Spain.
If you can't have clean sports, then don't bother! Allow athletes to take whatever drugs they wish. The playing field will be level again, and it's up to the athlete how much damage they wish to tolerate for a moment of personal glory. Or how much damage they wish to tolerate for not quite ever reaching that moment of personal glory... that'll learn 'em.