rxmd
May contain traces of nut
The problems arise when cheating is not easily detectable, so the rules are unenforceable.
I've often heard it proposed that the classic solution to that is much harsher sanctions.
Caught doping? Go to jail, and/or get banned from racing anywhere for a year. In all future races you have to wear a large black emblem on your jersey. Caught doping years after the fact? No grace period. Go to jail. Your victories are forfeit. You get an entry on the UCI's Cheaters' Blacklist. You pay a fine equal to several times the prize money for the race you were caught in. A competitor choosen at random gets the right to sleep with your wife. In short, you can choose to cheat, but it comes at a real and painful cost to yourself.
This would lead to an atmosphere of fear. However, at present the whole sport is already based on the premise that there is no respect for the rules, and that basically everybody is a liar and a fraud. I'm not sure which I'd prefer. (At the moment I'd prefer to watch something elseinstead.)