Sanji is definitely being sensible here. He hasn't done anything wrong. My issue is with how he is taking all this in. The thing that separated both Zoro and Sanji from the rest was their unwavering faith in Luffy and actively working for their goals if odds were stacked against them. This is the same guy who started smiling when Luffy picked a fight with Big Mom. It would be one thing if we were led to believe that Sanji was in any way less idealistic than Zoro or Luffy but honestly he isn't. It is uncharacteristic of him to act like this, like a defeatist. Sure a solution may not be immediately visible but there is always tomorrow. Even if for the time being he should stay here it doesn't mean his will to get stronger should waver. These are the same guys who will be the Pirate King crew. Let Luffy grow, and train yourself for even a few months and then lets see Big Mom try to contain you. Because even if you assume Luffy won't immediately come back for you (which I agree he should know better) he obviously won't forget about you.
Loki, I am not just taking this picture we saw today of him but adding it to his demeanor the past few chapters as well.
Well,sanji's wouldnt like to cause second "saobody" defeat which in this case would lead to death right away while marines would maybe capture everyone,but kill some.