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I take your line of reasoning, but I still think it's got little to do with morality.
You have to take a view. I'm merely saying that a clean rider doesn't not dope not out of the goodness of their heart but because they don't think its worth the risk. If you were to offer Team Sky some new supplement that wasn't illegal but offered a 1% increase in performance then they'd be all over it. Ergo, it's not the act of enhancing of performance that you're defining as immoral but the enhancing of performance by way of a substance that WADA has prohibited. Therefore, it is the breeching of rules you object to, not the desire to gain an advantage over a rival. I'm sure you'll accept that not all rules are moral and are very often based on practicality.
Initially, yes, unless they're a product of some government sports system and then they turn pro and likely give up further education or training to race bikes for money. Their income depends on results. "Rules" and this includes "anti-doping" ensures they are not cheated out of their income by someone breaking the rules.
Not just the riders - think of the whole British Olympic machine. It's funded and the funding is based on results. Imagine if you lot weren't winning because Russia just went "fuck it, give me ALL the drugs". Elite sport in this country would dry up. Knock on effect would be huge.