I'm very new to cycle racing, watches my first TdF this year, so by no means qualified to make a statement, but I do have question based on what I understand of the events all those years ago.
If they were all at it, then we're they not racing on a level playing field? If so did this not make the taking of drugs redundant?
Ok, simple answer is no. The so-called 'level-playing field' is a myth, or a convenient lie that can be used by dopers and their apologists to excuse cheating.
Not everyone was doping - do some Google research on Jonathan Vaughters and his time with Credite Agricole. They were a well known team during this period (sadly they folded a few years ago) and the team management were vehemently anti-doping. Also, Google Christophe Bassons and David Moncoutie, two well known non-dopers. So, simply put, they were not all doing it and those who chose to ride clean were disadvantaged.
Secondly, not everyone responds the same to doping. 'Lesser' riders, eg those with a lower Hct score (Google is your friend) stood to gain a great deal from doping with EPO. Riders with a naturally high Hct score gained very little. Universal doping would not provide a level playing field with everyone gaining, say, 15% on their natural base performance.
Thirdly, not everyone could afford the best doctors and doping program. Apparently Dr Ferrari (the best doping expert) would charge a small fortune and is alleged to have had an exclusive deal with Armstrong and USPS. So, if you were a less well off rider, on a smaller team, you made do with who and what you could afford. Doping was very expensive. Again, not a level field.
...and fourthly, apparently some riders and teams (LA/USPS) were protected by the UCI, so even if they turned up positive, the positive would be made to go away. Not a level playing field
at all.
I hope that helps. There is a lot of info on the internet, in fact if you read through the (locked) thread on here you'll pick up a lot of stuff.