Reading through the article and comments, it seems like there's a lot of confusion about what is considered "a user" and what typical dosages are. Obviously, a rave fiend who used to do MDMA twice a week and coke at least 5 and then moved to K would consume, completely disregarding this health but still staying conscious enough to continue dancing on a dance floor. At the same time, a tech worker who does Yoga, goes to Burning Man every year and have a long and productive relationship with psychedelics probably does a very K every 1-2 years in the right set and setting, but consumes a dose high enough to venture deep into the K-hole to seek some mystical answers — just as he does the same with DMT and other exotic Shulgin creations.

From the anecdotal data (including the tragic suicide note that pops up on HN every now and then) and sporadical research, it's very unclear how much danger does the second scenario actually entail.