You state - 'these side effects are so rare you only hear about them online' and 'neuropsychiatric effects of MDMA have been documented in case reports since the 1980s'
When you think about the number of users this section has (and site really) and the proportion of users suffering from these horror stories the numbers just don't add up. The cases you have reported are not from a single dose which many in this section report on - 'I took 150mg of MDMA 5 years ago and I'm still having xyz' again the numbers just don't add up.
I think one of the reasons why you hear about the adverse effects online and not so much IRL is that after the doctors have no answers and people are still having a really rough time months later, they tend to google and find bluelight. So to me the apparent disproportionate reporting of good experiences vs. bad experiences on bluelight compared to real life is simply due to being able to find bluelight and so forth with google. The adverse sufferers are certainly a minority but they are vocal thanks to search engines.
I have never actually seen specific data on the very old case reports of depersonalization after MDMA so I can't tell you if that was after many uses or not, but I think the key thing to remember is that people have severe mental illness drugs notwithstanding - some people might be right on the edge, and the people that have increased risk of adverse effects after MDMA (a particular serotonin transporter gene) have increased risk of depression, anxiety and PTSD after stress, and acute tryptophan depletion leads to depression in this population, whereas other people without this gene don't react negatively to tryptophan depletion as far as mood. Not everyone is the same - there is an extraordinary degree of variation from person to person, especially variation in the pre-frontal cortex.
Think of how different everyone's personality is. One person has autism spectrum disorder, another is neurotypical. One person has seizures, another person has bipolar I. One person has schizophrenia, and another person has the ability to solve 313 x 267 in their head. Are we expecting MDMA to change neurophysiology the exact same across all those populations?
So I don't think these adverse effects (including HPPD) are like serotonin neurotoxicity where we would be expecting it to be related to cumulative use over time - a powerful shift in the brain's network could certainly happen after one trip even after many previous normal trips. Persistent altered states of consciousness (sugar coat for "psychosis") after one dose of LSD are noted for example. I can name other examples of a persisting change after an acute experience, especially if we go down the PTSD or addicting drugs route.
But I would argue that the majority of the severe adverse effects sufferers were actual abusers or were under special circumstances. I don't think that the one dose/one time people make up much of the severe adverse effect sufferers population.
I've been told recently that the brain's circuits are often multi-modal (this was in the context of discussing HPPD). That is to say that they can have different operating states - where one state can be "normal", another state may correspond to HPPD-symptoms (which occur in drug naïve people). I don't think its unfeasible that psychedelics can flip someone into another state and it takes a while to flip back. People could have significant individual variations in vulnerability to flip modes in the first place.
The stories of depersonalization after cannabis use seem to occur primarily within the first few uses - this was true for my friend who had it happen on her first use. Depersonalization for months ensued. Although I had no idea what it was at the time, I now realize her description of things matched depersonalization exactly, and depersonalization after cannabis is indeed noted in the literature.
I have stated before that these threads do more harm than good - of course there are side effects, of course people can run into problems but when you look at the amount of people taking MDMA each week if a side effect was these types of problems from a single use the drug wouldn't be as popular. Without going online - if you knew anyone that had a serious side effect as stated in this thread would you take the risk? So friends of friends, friends of them, stories in raves, clubs etc. I have never heard such a story in real life.
I'm certainly not saying it is a safe drug and it is not without risks.
One of the reasons why I compared these adverse effects to anti-epileptic skin reactions like SJS and TENS is because they are probably ballpark in that same category of rarity.
Not to get political, but there had been some talk of the removal of phase III trials under the guidance of the Trump FDA appointee (he apparently wishes to do away with phase III). After asking if this would have significant consequences, I was told that safety isn't even evaluated fully until phase IV, and that phase II/III often only catches the common side effects, and the rare side effects can be missed until phase IV with the drug out on the market.
If under controlled situations with large populations (phase III) rare side effects aren't often caught, I certainly would expect some
serious trouble detecting the rare side effects of
illicit drug use. Yes we can do a study in people who have +300 lifetime uses, and we can see this and that about their brain or cognition, but the cases where people get severe adverse effects after a bad weekend slip through the cracks. I've never even been able to find a single neuroimaging study on people with HPPD, yet it is indeed a DSM diagnosis and recognized clinical entity. We essentially have to take what we can get at this point as far as data about these rare adverse effects, and people posting on bluelight is a piece of (anecdotal) data that we shouldn't cast aside just because we're in the day and age of transgender mania type stuff.
"I have stated before that these threads do more harm than good"
I personally don't seem the harm in this thread especially. I hope OP is okay with me writing this, but they have attempted suicide twice in the last 7 months (since these adverse effects after months of ecstasy abuse) and would like to hear stories about people recovering. What's wrong with that?
There is a complete disconnect between the people who have/have had the adverse effects and the people who haven't. Because the adverse effects are so rare and are mostly reported online where the minority can be vocal, this is one of the few places in which the OP can get support. The adverse effects sufferers certainly don't get support from their friends that keep on using drugs and wonder what the hell is wrong with their friend because "I took the same drug and I'm fine so there must be something wrong with him, it can't be the drug that I gave him that caused it".
Doctors oftentimes don't connect with their patients on this matter because they are used to dealing with hypochondriacs and immediately throw these patients into that category. Their families don't understand it because they are oftentimes pretty drug naïve or unaccepting of the person in question's drug use. People lose their friends, jobs and significant others over these adverse effects, just as you could lose all that with a regular DSM mental illness.
While the clinicians urge people with various illness to attend support groups, I'm not aware of any local substituted-amphetamine-depersonalization support groups, so unfortunately people kinda just have bluelight. Although I fully support seeing a psychologist/social worker and trying CBT et cetera.
I totally get that there are endless "help I took too much MDMA threads", but this thread in particular seems like a helpful one for the OP to hear about recovery stories... The people talking about just accepting "irreversible brain damage" and then comparing that to a shoulder injury aside.
Sorry for the novel, and I hope I don't seem argumentative. My life really got turned upside down to say the least by severe E abuse when I was 14 so I'm just very passionate about it. And for what it's worth, I have heard a couple stories IRL since then, particularly one of insomnia after E abuse.
There is a lot of room for people to try and say "You had pre-existing issues and now you're blaming everything on the drug because you can't deal with your life". 
