@Sereques:
Robin did not talk down the SHs. All she was they should leave. That was a great course of action considering her fears for them. I mean, how can she know they can take down the whole of CP9?
Sanji on the other hand is aware of the strength of the crew. A smart course of action is to tell them nicely to go back and with a sad face. It's not like the family are not aware that everything they're doing is against Sanji wishes. The drama and belittling of the crew only point to the idea that he has a plan. Else, then Sanji is very stupid.
Yes, because Sanji is going to tell the Straw Hats to just leave a Yonko's territory and easily subject themselves to an attack. Yes, he knows his crew's strengths, but as I stated earlier, he is not about to have them risk death because of him.
So, Sanji has two options: he can play the Vinsmoke card and fight the Straw Hats, thus giving him control over their fate. Or he can weakly tell them to leave and easily open the Straw Hats to external attack. I don't know about you, but the second option seems far more pitiful.
And isn't it BETTER if Sanji doesn't take the same course of action as Robin? They're different characters in different storylines, after all.