That is frustratingly ridiculous. You are cheating to gain a competitive advantage over your peers, and thereby deny them winnings, sponsorship, adulation, etc. It doesn't matter if 90% of people are doing it (which I don't believe they are)- you are still cheating the honest 10%. Doping IS morally wrong and the people who do it disgust me. Like everyone else, Tyler Hamilton stood in front of the public and deplored cheats while he was himself engaged in some of the most systematic cheating we have had described. This is not something a 'good guy' would do, regardless of anything else he may be doing in his life. He is a deceitful hypocrite who should be prosecuted criminally for stealing from the clean athletes for years on end. It is a horrible injustice that he still has his Olympic medal.
The thing is you can make a very compelling argument that morally doping isn't wrong. Who do you harm by doping?
As for likening it to cheating on tests: every point you made was flawed. The stakes in professional cycling are so much higher, as the fact that you might gain a small competitive advantage over someone in a test is unlikely to have a significant effect on the rest of either of your lives. That said, cheating on a test is also morally wrong. You won't find many 'compelling arguments' that it isn't morally wrong. This IS black and white, and so is doping. We're not talking about some guy with no hope of making a living any other way- we're talking about a guy who probably grew up in affluence with every luxury. A spoilt kid who can't stop cheating because he isn't good enough on his own.