It's simply not healthy to snort stuff through your nose, that's all.
I don't know if snorting MDMA is worse than snorting cocaine, but putting anything up your nose isn't the best idea. It's good for a quick onset with a little rush, but not necessary.
If you still have MDMA in your nose in the morning that means you're not snorting it very well! You should inhale the entire line through your nose, with minimal drip.
I wouldn't necessarily recommend snorting anything to your friends, but everyone can make their own decisions. I don't see how snorting MDMA is any worse than snorting cocaine, al though it may be.
You and your friends should try out parachuting Molly when you want to extend the high later in the night and if you like the quick onset of snorting it.
Just definitely never snort pressed pills! And if you're going to snort MDMA, I would never even think of it, unless it is very pure MDMA crystal.
Molly is often cut with stuff you don't want to snort.