Question:
The hypothesis (in a nutshell) is: there are no MDMA users that display the symptoms that are consistent with the brain damage that is supposed to be caused by MDMA (in fact, an symptoms tend to be opposite of what is expected - an decrease rather than an increase in aggression) Might you be thinking of the notion that some studies of aggressive offenders have been found to have lowered levels of serotonin? This is a far cry from the claim that brain damage causes increased aggression.

Answer: Fenfluramine is not an MDMA analogue. It's just a drug that shows similar levels of serotonin reduction (which they suspected may equate with damage) to MDMA. Personally, I don't think that the serotonin reduction alone is that significant. Much more worrying is the more recent research that has demonstrated actual physical damage in rats and lower primates.

I'm not making the claim (or even supporting the claim) that MDMA users are suffering from brain damage. However, I'd be interested to know where you get the idea that increased agression is the only indicator of damage. I rather think that you wouldn't really know one way or the other unless you did CAT scans, or whatever the clinical tests to determine damage are. LSD first crosses the blood-brain barrier, where it finds itself some serotonin receptors to snuggle up against. It activates those receptors (partial agonist) and this causes a decrease (if i remember correctly) in PI turnover mediated by g-proteins. These changes in PI turnover can result in phosphorylation of proteins, and various biochemical changes which can result in changes in how ion channels open and thence to changes in the polarization of the neuron. Ultimately, resulting in a change in the firing rate of the neuron and a change in the overall pattern of neural activity in the brain.