You can artificially inflate the levels of a "natural" substance to the point where things get dangerous. Too much EPO can thicken the blood and a few guys died from heart attacks in the early days. True, guys have learned more about how to take EPO without dropping dead and there's not a whole lot of risk with a good doctor on hand, but what kind of effect does pumping artificially thickened blood have over a 10-15 year career?

It's just not a good idea to basically force young guys to either take drugs or quit the sport. There are going to be side effects for any drug. What happens to the kids who aren't under a doctor's supervision? Just look what happened to Ricco.