Any idiot can make a respectable comparison between the harm caused by MDMA and that caused by addictive illicit drugs.
I'm not so sure anyone can yet. Heroin, for example, does not cause brain damage however it can cause great harm to the person and the community through lifestyle issues related to acquiring it illegally (impure, dealing with dodgies, price), having to acquire the money and health problems related to lack of regulation.
MDMA...lets have a look at this in 5 to 10 years time and see where our regular users are. MDMA does cause brain damage. In the short term this includes (but is not limited to) symptoms such as bad memory, slurring of speach, inability to concentrate and shorter attention span. And these are just in my experience! Productivity had gone way down and in a different industry this could be very dangerous.
Or are you wanting to simply rate drugs on their potential for addiction?