The biggest problem isn't that the highest-level athletes would waste away their bodies (that's a big problem, but not the biggest); it is that below them, there will be thousands if not millions of second- and third-level athletes doing the same. With much less control.

Imagine if every kid out there that wanted to be the next Ronaldo or Neymar (and could afford it) started taking steroids and EPO. That's a huge cost, and what did we gain exactly? A slightly lower number on some clock?