MDMA isnt as toxic as most people think it is. really, in the short term youre talking about potential overheating, depression a few days after etc etc but really, most of the danger that comes with taking ecstacy comes from not knowing how much youre taking, and also, taking what you think is ecstacy but is some other more dangerous drug, like PMA or something like that. long term youre set up for some depression, though i havnt seen a convincing study that guarantees it happening, putting yourself at risk of a bunch of mental illnesses, but really it isnt a life or death drug. id be a lot more wrried about someone taking coke or morphine, and thats fairly common.
overall what can i say, taking those sorts of drugs unsupervised is a fairly bad idea in general, but i doubt that it will kill him if he takes proper precautions ie taking teh same pill from the same batch, keeping cool, keeping appropriately hydrated, making sure he doesnt approach dangerous levels of depression a few days after (ie suicide risk) and that sort of thing.
just bloody legalise it imo, take out the criminal element, and let people fry their brains if they want to. bunch of meddling bastards