I get the idea of punishing the people who have taken medals and money from those who are clean, but I also think that in order to have a lifetime ban for a first offense (lifetime bans exist for multiple offenses) the whole system is going to have to become far more airtight. Jail offenses to me require an even higher burden of proof.
First, the science of what substances actually enhance performance needs to be a lot more solid. This would require a much higher standard of guilt than is currently used.
Second, the detection process needs to be rock solid and virtually unassailable.
Third, the labs need to be much, much better. In just the past 2 years look at the number of labs that have had their accreditation pulled. Now I could argue that that is a good thing and that WADA is holding them to a high standard. An attorney (I am not one) could argue that the tests done before the accreditation was pulled are tainted. "Just how long has the lab been out of compliance"? (This is a common tactic in blood DUI cases or even radar guns for speeding tickets is to check when the equipment was last validated).
Fourth, the chain of custody needs to be airtight. For instance, I was rather close to a doping control officer who would collect samples and call the courier who would meet her at our house to pick up the sample. Now it was never really out of her sight, but I bet someone would try to poke a hole in that. "So DCO Jones when you went to the bathroom did your BF have access to the kit?"
As for the OP question about criminal charges for PED use, well just look at our laws on recreational drugs. Cocaine is illegal. Steroid use without a prescription is already illegal. But I am not sure that throwing a steroid user in jail is the way to go either.
The idea of WADA was to circumvent the need to try to get 200 countries to have the same identical laws.
People often point to other professionals who have licenses to practice pulled. That does happen but the bar is pretty high. A felony conviction (again a very high bar) often triggers that loss of license as can a misdemeanor in some cases or at least several of them. Or the hearing to disbar a lawyer for instance is a lengthy process as well. (Often these things are done as part of a plea bargain with prosecutors).
I also suggest you follow Roger Pielke Jr. He has written extensively in this area and responded to several of Nick's tweets with good practical stuff like do you really want an American athlete competing in Russia to be subject to Russian laws in this area?