I don't really care if any one of them uses PED. It would not change my opinion of them because they are all great athletes and I'm sure that no matter what kind of substance they might be using it hasn't miraculously turned them into super humans. There is still hard work behind it all.
The rules in place against certain substances are an arbitrary system. What might be banned today, could easily be allowed tomorrow. So who is to decide what is wrong, bad, good etc.? All it takes is a change in perspective.
I would allow it. Demonizing certain substances only results in pointlessly judging great athletes who most likely would've stood apart from their peers anyway, with or without PED.