Dude! Smoking MDMA by itself is not even a good idea. While it is possible to smoke pure crystals from a suitable pipe, even if you're very careful with the heat a lot of it will burn off. Not only is it a waste of good crystals, the smoke tastes awful and makes your throat feel as if it's being stabbed by lots of tiny needles. Any effect you get is very harsh with a brutal, jagged comedown. This is why I used to think smoking crystals was the worst way of taking my beloved MDMA.
However, because of Valleys I've had to modify this list to include "smoking crushed pills without a pipe", which replaced smoking crystals as The Very Worst Way To Consume The Very Best Drug Of All Time. You probably want to know why.
A pill weighing 350 mg and containing 150 mg MDMA also contains about 200 mg of filler. This filler is usually lactose, microcrystalline cellulose or cornstarch. In pharmaceutical drugs this is the case at least, I presume illegal MDMA manufacturers use the same or something very similar. Because this filler is mixed very tightly with the MDMA you'd have to burn off/evaporate the filler to be able to evaporate and inhale the MDMA. Unfortunately, at the temperature required to do so all the MDMA has already decomposed off so at this point you're basically smoking burning sugar pellets. When the filler material is tightly packed like in a pill, it doesn't burn easily and produces lots of nasty complex carbohydrates. Quite a few of these are strongly carcinogenic.
So while you thought you were smoking MDMA you were inhaling a ugly mixture of combustion products, random carbohydrates that could give you cancer, some very fine sugar crystals that irritate your airways and whatever is produced when MDMA burns/decomposes. There is a chance a few lucky molecules can escape the carnage and enter your lungs, but you don't really deserve these.
Damn man, thinking about someone burning MDMA almost makes me cry. DON'T SMOKE PILLS!