Bullshit. Zoro straight up said they would have had no faith in him as captain if he had that reaction with ussop.
Sanji’s case was not like Usopp’s. If he didn’t fight Luffy and tell him to leave, Judge would take action.
1)He would blow up Sanji’s hands. (Even though bracelets were duds, Sanji thought they were real.)
2) Vinsmoke brothers, along with enraged army, would gang up on Luffy, Nami and Sanji.
3) Judge would order Zeff’s execution.
4) After trio were captured, Judge probably wouldn’t deal with torture stuff and would directly want Luffy’s head.
Sanji joining the crew is not equal to “I abandoned everything related to my past. Zeff is nothing to me anymore.”
What Sanji did wasn’t right but he thought that was the best. Dude even broke a deal (although it was a facade by BM’s side) to become a slave in exchange of sparing Luffy’s and Nami’s lives.