To sell a case to a jury, the prosecution likes to have a clear narrative that explains just about everything. In reading the existing commentary from both MSM and blogdom, I imagine the story goes something as follows. Remember -- this isn't my opinion, but what a prosecutor might say.
Floyd left his sheltered upbringing and came to pro-cycling as a naif. The rebellious nature that led him to drink beer and Jack Daniels added slack to his moral anchor, and the cesspool of the sport may have carried him far away. He developed a Machiavellian personality, showing a surface of "Good Old Floyd" while darker things happened underneath. After stage 16, he was a desperate man facing the end of his career and his dream, and reached out for something that would feed a last attempt to get the glory he believed he deserved.
However, we need not look at his morals or intentions at all, only the facts. He had whatever it was in his body. A fact. Whether he took it knowingly is immaterial -- it was in him, and it fed his rage and helped him do what no-one believed was possible. This changed the outcome of the race, which is the worst sort of result, and it cannot be allowed to stand. We cannot allow our imagination of whether he could or would have won the stage without this chemical to affect our judgement. He had the exogenous material, which is not allowed, period. He must be held to our strict standard of accountability.
My opinion: If it is exogenous, the game is over. If not, then the arguments of the endocrinologal defenses come into play, and there is more relevance to the character assasination in the first paragraph.