I note first we are willing to make distinctions as far as enhancement is concerned for athletes that we don’t make for soldiers (ref: Dexedrine use by Air Force pilots) or for students (who increasingly use performance enhancing substances like adderall and coffee).
Second, I note that there are possible invasion scenarios for which we face a shortage of soldiers with highly specialized physical abilities. I claim first that we have a natural pool of these kind of recruits in professional athletes and second that in doomsday invasion scenarios where there is a premium to be placed on the physical skills and endurance necessary to perform highly specialized tasks we want to have the ability to select for specific traits and want to absolutely maximize the expressions of those traits. Under these circumstances there is no counterargument for legalizing and using performance enhancers and indeed much depends on the state of the scientific knowledge base that we can access to inform those efforts.
That’s why we should legalize performance enhancers. There are several parameters that need to be set, for instance, the nature of the optimal regulatory framework, and how professional sports leagues should react to chances in these laws. But note that this policy carries a positive externality for athletes: it allows them access to the legal and scientific remedies that they don’t have access to in a world where they necessarily and exclusively bear the totality of the physical, emotional, and financial tolls that come with using illegal performance enhancers now.