BME/HARD is the adult/erotic wing of BME. It was founded in 1998, in BME's 4th year (and the year after BME/extreme was founded). Since the day it was founded, BME has been getting adult photographs that were not appropriate for public posting. Due to the nature of these photographs, as well as the huge amount of bandwidth required for all the hits they would surely receive, a special subsection was needed.
It was clear that there was an interest in the subjects and an overlap in the enthusiasts, but, knowing that it would represent a fundamental shift in how people perceived the site, it was some time before these sections were officially included.
After reluctantly adding BME/HARD to the site, it turned out to be a perfect match, and BME/HARD has been an important part of BME's success. This is both due to the fact that it is a pay site, and thus helps pay the bills for the main site, and because it is the only site to cover these topics without pandering to the lowest common denominator.