It is very hard to go an agreement on a matter with a people who don't have enough information about that topics. Moreover some people are like penny wise pound foolish. They don't want to take risk and always try to use risk free profit. But there is no option to make a risk free profit without no arbitrage principle.
Anyway you wrote well.
Risk free profit - it is a funny thing to consider, isn't it? Useless to spend too much time on though :)