I don't know enough about the science of PEDs to say how natural or unnatural they might be. For some, it probably comes down to side effects. Steroids for example have known negative side effects for people who use them, and I think it's fair to say that we want our sports to be about more than wrecking your body for the sake of fame and money. But I imagine there are PEDs that don't have such side effects, and if there aren't there probably will be someday. But even then there's an ethical backdrop of fair play that is inherent in our sports. Yeah, there are a lot of people who don't put that into practice in the actual game, but I think that by and large the society that supports these games and makes them possible has an expectation of fair play and natural talent. Equipment and training improvements are available to everyone, while PEDs, even if they were available to everyone, would not be used by some due to the moral and ethical issues involved. I'm personally okay with the idea that sports should encourage natural talent and should not force people to take drugs in order to succeed.

In the end, whether or not PEDs are natural or not maybe isn't the issue. Not everything that's natural is good. We don't see people loading up on snake venom and chlorine, after all.

That said, there may come a time when society as a whole, and all of the athletes in any given sport, are more comfortable with that sort of thing. If there aren't negative side effects involved, and if a level playing field can still be maintained, then that may be the day when sport changes.