Based on analyses in at two countries, fake MDMA (ecstasy pills without MDMA) is not common.

MDMA content in the pills is often overstated, but still high (even too high, referring to the health organization guidelines); this is IMO the most damaging effect of lack of regulation - it's impossible to know how much MDMA one is going to ingest.

I agree 100% that MDMA legalization is a benefit. As first step though, drug checking centers are a huge (and realistic) step forward.