I got into an argument with a friend on MMA fighters and said that any fighter that gets caught PEDs should probably have an asterisk by his record. His defence was that could I say for sure that other fighters aren't using PEDs just because they haven't been caught. All that means is that they haven't been caught.
This kept going in circles and I kept saying that you can only go off what evidence you have but he kept repeating and then we just dropped it. I'm pretty sure his argument has to be logically flawed and was hoping for a better explanation of why.
Sorry I didn't respond sooner. I thought some more about the conversation I had and I didn't structure my post properly. So when I said that the MMA fighter should have an asterisk next to his record, he argued that they shouldn't and those wins should count because you can't prove that others weren't cheating. What I'm having a hard time with is explaining that you can't make decisions about things you don't know. If the other fighters are using PEDs, and we have evidence then they should get punished too, but until then you shouldn't punish nobody because you can't prove others aren't using.
At this point I'm not particularly looking for a fallacy but I just want to know if his way is a valid approach. That you can't punish fighter X because fighter y is also cheating but just got lucky and wasn't caught.