Im going to speak from experience here, I consider myself a responsible user of MDMA, and I researched extensively on bluelight and other forums as well as other websites on MDMA and I didnt have the most remote idea that there was lethal dosages of mercury in some batches of MDMA, I always test my drugs with multiple reagents made by myself, as well as trying to only purchase from reasonable connects, I personally speaking from myself I would have never in my whole life touched MDMA if I knew this was even possible and I personally know that if people were informed of this as rare as it might be most people would never touch this substance, that would be akin to saying:
Some samples of cocaine might contain lethal dosages of cyanide, we dont even know how frequently it happens, so its a russian roulette every time you take cocaine, the possiblity might be vanishingly small or high, we dont really know, but it exists so take your own decision.
Do you think people would keep taking cocaine or even try it at all? I guarantee most people would never touch it, and if this is true after all then absolutely yes some people with "long term comedowns" are actually people poisoned by mercury, and thats not counting people that have died from mercury toxicity due to mdma if this really happens, so what im trying to say is that we need to clarify this topic and if it really is a topic we need to make the information get out to users and warn them, I personally researched a lot about MDMA and I read a lot on it, I always test my drugs with multiple reagents and I thought I was safe, and I didnt even know about this, and thats me who researched this intensively, the absolute overwhelming majority of even harm reduction users of MDMA do not know about this and we have to get this information out and clarify this topic if its for real.