Everyone deserves a second chance. 2nd offence should be lifetime Olympic ban though (I'm looking at you Gatlin).
Blame CAS. They seem to take the side of the dopers more often than not, like overturning our ban on former dopers representing Britain at the Olympics. Dwain Chambers, for example.
I think you need to look at the circumstances on how a PED got in to the system. There is deliberate doping and there is the unintentional ingestion of minute traces of PEDs which can happen quite innocently by cross contamination in the supplement factories. You can buy stuff which will get you a ban in Tesco. There is also an issue that are some PEDs on the list actually performance enhancing. The most common PED is legal and most homes have it. Good old caffeine. Deliberate doping should be a life ban.
I used to love athletics but you'd have to be naive to think that a lot of them aren't doing something illegal to give them the edge, something that isn't detectable yet.