My argument is that there are tons of legal substances that are lethal in the wrong doses. Most people who use drugs recreationally are not suicidal, and therefore do not willfully consume drugs in high enough doses to kill them.
Deaths from ODs are often caused by mistakes, which are much more likely to happen when a drug is illegal and it is hard to find out the exact potency of whatever it is they're going to use.
Potential death is not an argument for keeping a drug illegal, because if someone wants to kill themselves, they can do this with OTC painkillers, and potential death is clearly not something anyone cares about when they drink alcohol, so why should they care about it when it comes to ecstacy? Why should my drug of choice be banned for a reason that someone else's drug of choice (alcohol) isn't banned for?
As far as I know, deaths from MDMA alone are extremely uncommon, and when they do happen, it's usually because of hyperthermia you are at higher risk of getting while on MDMA. However, it can easily be countered by consuming greater quantities of water. It is also not unheard of that people try to sell things that aren't really E as actually E, causing the user to consume a substance they aren't familiar with, aren't physically used to, and don't know how to dose properly. That's another thing that you can more easily avoid if you can easily trace the drug you purchase back to its manufacturer.
