The second major misconception is that MDMA causes Parkinson's. The original study was retracted because the drug manufacturer mislabeled the MDMA bottle as Methamphetamine, a completely different drug. They gave the Methamphetamine to monkeys instead of MDMA.
I would recommend checking this out: http://www.youtube.com/watch?v=XjvNCijeYlI
Skip to part 3 if you're wanting to get to the scientific studies.
PS: My mother has a PHD in neurology with a focus on brain development and MDMA is the drug she was most frightened of. Not that that actually means much in the grand scheme of things, but she has done a lot more literature review of MDMA than I or I suspect anyone on HN has done.
Edit: can you please link up the studies you're referring to?
It's not even so much that (comparing two drugs like that doesn't really make sense). It's that the dosage administered was far more than what would be comparable for methamphetamine. 6 mg/kg of one drug is not necessarily comparable to 6 mg/kg of another drug... 300 mg of methamphetamine for a ~110 lb. person over 9 hours is absurd - the maximum prescribed dose of Adderall (d-amphetamine) is generally 40-60mg per day, and that's only for individuals with high tolerance (or very severe problems such as narcolepsy). These are oral dosages, mind you, whereas the study used subcutaneous injection, which amplifies the effect of the drug further. Then account for the fact that methamphetamine crosses the blood-brain barrier more easily than its cousin that lacks the methyl group, and you start to wonder why only one of the five monkeys died.
Even before they realized the drug mixup, the Ricaurte, et. al. study is so flawed that it's almost laughable that it was published in the first place. Your study is intended to simulate the environment of a club/rave? 20% of your subjects died after what you considered to be a moderate dose, and you didn't think that was cause to question your methods? Raves may not be the healthiest places in the world, but if real life were anything close to what those data suggest, the morning after a concert or rave you would find the floor literally covered in dead bodies.
I won't even get into the absurd conclusions that they draw from their measurements themselves, since this is HN, not a neuroscience forum, but suffice to say that any college freshman in an introductory neuroscience class should have known better. It's as if they copied and pasted the analysis from another study and inserted their own data into it - that's how nonsensical it is.
The retraction for Ricaurte, et. al.: http://www.pages.drexel.edu/~ls39/peer_review/Ricaurte_retra...
(The original study is linked from the retraction page; I'd emphasize again that the study itself had enough other flaws in it that it should never have been published in the first place, even if the drug mixup had never been discovered).
The real problem is the way the studies were conducted. They didn't test hair samples to verify whether the participants used MDMA, much less control the environment it was taken in. The largest study I referred to that was done by Harvard Medical was done on people who had never tried the drug before, were not at raves taking drugs which could not be verified for purity (amongst other problems like dehydration and hyperthermia), and they verified their study through hair samples.
https://en.wikipedia.org/wiki/File:Rational_scale_to_assess_...
http://www.globalpost.com/dispatch/news/regions/americas/can...
"12th death linked to tainted ecstasy in Alberta, B.C."
http://www.vancouversun.com/12th+death+linked+tainted+ecstas...
"8 Alberta deaths linked to ecstasy-like drug"
http://www.cbc.ca/news/canada/calgary/story/2012/01/31/calga...
This is especially surprising since God explicitly told you not to eat pork almost 3000years ago.
Remember kids, pork and shellfish are evil - just so no.
One study of 52 users that where hand selected out of 1500 that showed no cognitive impairment. http://www.addictionjournal.org/viewpressrelease.asp?pr=147 Others studies both before and after have demonstrated issues. The problem is it's hard to find good data on individuals before they started heavy use, and sleep deprivation and dehydration are linked to long term cognitive impairment.
However, if you look at the existing literature there is no large scale and long term study's demonstrating it's safety. And a lot of evidence that MDMA is dangerous.
Going to prison.
Putting people in prison for harming themselves is the height of absurdity.
Furthermore, these risks must be balanced against the very tangible and easily observable psychological benefits. There's a reason psychotherapists used this drug.