I think the effects you're describing are mostly all the result of developed behaviors / personal neglect from taking large does regularly. Taking high doses of, ex. Adderall for two years would likely have similar effects.
I do feel differently about marijuana, ecstasy, benzodiazepines, mdma, etc. They don't seem much different from alcohol, which we openly condone, despite the obvious issues. At least none of them (mostly) destroy lives in the span of a few years.
Opiates are somewhere in the middle for me. Legalization seems dangerous, but not as obviously stupid as for meth. It's in the same category as crack for me. No real casual/functioning users, really, just almost inevitable misery.
That said, I would still support its legalization as long as it could only be administered in controlled environments.
> As of 2015, the long-term effects of MDMA on human brain structure and function have not been fully determined.
MDMA in itself isn't as bad as other drugs, as has been mentioned. It's the compounds that it's cut/mixed with that poses most of the immediate dangers. In fact, the therapeutic potential of MDMA is reason enough for it's rescheduling.
I'm not saying MDMA is as bad as other drugs, nor that it should be illegal. My cousin's uncle's daughter's brother has taken it several times, and he thinks it definitely has a lot of potential for therapy - can't attest to PTSD, but he can absolutely see it working for couple's counseling.
What I'm saying is that it shouldn't be something you can pick up for $5 at the gas station. If MDMA were legal, I would want there to be some pseudofed-like limit to how often you could purchase it (one dose every 3 months is generally considered safe), and I would also want it to be required to take the drug immediately after purchase.