I have said this several places, but I think it meet to summarize. There are two essential claims behind the idea of spelling out when exchanges are "euvoluntary."
1. The state is never justified in interfering with euvoluntary exchanges.
2. Even if exchanges are not euvoluntary based on condition 6 (disparity in BATNAs), interfering with exchange often makes the worst off, EVEN WORSE OFF. This point is made many places, but you will find it made well, and often, over at "Blunt Object." BATNA: Speak it, understand it.