Say one of your kids becomes so great at cycling, that he wants to eventually do it competitively. He does well, but lacks the edge that all the others have because they chose to dope. So basically, with his back against a wall, your son has this decision to make:
1) To dope, succeed at his chose sport, but most likely die at a relatively young age
2) To not dope, and know that he'll never succeed in his dreams of becoming a champion, let alone finishing in the top tier.
Me, I don't wish to impose this on our future generations of athletes, let alone my child. I think you'd feel the same.