Juan: Unlike the ancient Olympic games on which they are based, the modern Olympics include professional as well as amateur athletes.
Juan's Conclusion (hence)
Having pro athletes violates the spirit of fairness.
Juan's Intermediate Conclusion
It's unlikely that amateurs will offer a serious challenge to any pros they face in their events.
Juan's Premise (since)
Amateurs rarely have the financial resources available to pros.
Evaluating Michiko's Response
She says pros should be able to compete. So she seems to disagree with Juan's conclusion. Does she disagree with his premise or intermediate conclusion? Not really. She's just saying that the point of the Olympics is to showcase the best, so if pros have more resources and that makes them dominate amateurs, so be it. They're the best; we wanna showcase the best; so pros should be at the Olympics.
Goal
Let's find an answer centered on whether or not pros should be allowed to compete at the Olympics.
Since that disagreement was so obvious and explicit, the answer will probably get at the underlying premises. Juan thinks they shouldn't, because of fairness concerns. Michiko thinks they should, because of concerns about showcasing the world's best.