I was at uni during the meph boom, and there were lots of kids who looked down on my use of cannabis because it was illegal but who were hoovering down that shit.Meph's success was due to a total lack of coke or E, that it wasn't regulated whatsoever and the price, which made it not only the drug of choice for a lot of people but also gave people easy access.
I don't for one second believe there was a huge untapped population that, Meph aside, would be 'normal law abiding citizens.' From anecdotal evidence, the people taking Meph were younger people, without access to (lots of) money nor dealers, who'd had exposure to drugs already.