Indeed it all boils down to hard work.
Unfortuantely the way modern sport has developed in this market driven world, and not only in cycling, is that athletes are constantly having higher and higher demands placed upon them to become faster, stronger, better, etc. As old records (set by doped athletes) are broken (by doped athletes on the next generation of PEDs) and new standards of excellence are set, it has become natural for athletes to look elsewhere for that edge that without the help of science would be otherwise impossible. Take this with the prospect of acquiring fame and great wealth and the illicit culture with all its possible detrimental health consequences becomes a system within which a developing athlete gets sucked into at an increasingly young age. So that what used to exist within the realm of trying to "beat the world record" has now become a modus operandi even for the teenager in seek of finding self esteem, or the master category racer to feel at one with the pros and conquer the frustrations of his/her own short-comings.
Science, human instinct and the business market (which demands results at all levels) have created the monster. This is why I find it nearly impossible to believe that these guys are clean.