A musician is free to take beta-blockers to control stage fright. These drugs function in the exact same way as performance-enhancing drugs in sport. They lower the heart rate and blood pressure and allow for a better, more measured performance. 
Professional sport is part of the entertainment industry. Millions tune in every weekend to watch sport because it provides entertainment. It should, therefore, be treated in the same way as other entertainment industry sectors. Doping does not detract from the entertainment aspect of the sport. If anything, it enhances it by improving performance, pushing the limits of human ability, and thereby providing a better spectacle. In the same way the musician takes beta-blockers to coax out a better performance or a writer may consume drugs to produce their best work, athletes should be permitted to dope to improve their physical performance.
[P1] Sports stars are entertainers. [P2] Other entertainers are free to use drugs to enhance performance. [P3] Therefore, athletes should also be free to use drugs to enhance performance.