That's why stories such as the Slaney one are so shocking and disappointment. Like anything in life, there is some gray area involved in these matters. A nationally ranked athlete once told me that coaches were the primarily culprits. This athlete insisted some runners had no idea they were even using illegal substances. The USOC banned substance list is a very long one.
Caffeine is an illegal substance, so is ephedrine, which is found in over the counter cold medicine.
Clearly, drinking coffee is far less flagrant than injecting Hgh, but rules are rules. If you can beat the system but taking masking agents or clearing your system before competition, the rules will not prevent you from winning medals. You can take the subway in the New York or Boston Marathons too, and if no one catches on, you can get away with it. In the end, sports such as running are a test of athletic skills. To cheat in any way harms the sport in an irreparable way, however small.