People often feel the need to rationalize their dishonesty. The danger is taking that first step.
The story of Joe Papp, an Olympic cyclist falls into this category. Papp consulted his physician, who wrote Papp a prescription for erythropoietin (EPO), a cancer treatment that increases the production of red blood cells. Papp injected himself, but also imported and distributed EPO to his team and to other teams. This essentially made him a drug dealer.