User blog comment:Kaido King of the Beasts/Chapter 844: Always a Dump Guy/@comment-24850639-20161027162929/@comment-71.13.82.131-20161027183524

The difference between the Nami, Robin, and Sanji situations and the Ussop situtaiton is that Ussop was trying to go against Luffy in making decisions and doing so with no outside involvement. Zoro fought along for Nami and Robin because he was tryin got free them of their "capture" to allow them to make their own decision. Ussop was not being held or associated with anyone else when he expressed his desire to separate. I would expect from Zoro's previous actions that he would free Sanji of any ties prior to truly accepting what he says as his true desires.