Ok, I know there has been some controversy over Zoro’s attitude toward Sanji here and I’d like to share my thoughts about it. I also think Zoro’s evaluation of Sanji’s decision was a bit too harsh and I didn’t know what to make of it at first. Now I’ve come to my own conclusion and it’s mainly twofold: 1. Zoro has once again shown how level-headed he can be when it comes to keeping the crew down to earth / 2. But when it comes to his opinion about Sanji, not so much.
As a zosan shipper I did want Zoro to show some concern over Sanji. But that doesn’t mean I disapproved of his point that they should focus solely on Kaidou. In fact that’s exactly why Sanji left by himself - so the crew wouldn’t be sandwiched by Kaidou and Big Mom any time soon (though he might be aware that Luffy would eventually come after him). By reminding the crew about the situation Zoro is respecting Sanji’s motive (not his actual decision though - this point is important) behind leaving alone and Sanji wouldn’t have expected any less from him.
However, understanding Sanji’s motive doesn’t stop Zoro from being pissed. Hell he’s pissed alright - look at the vein popping on his arm as he insults Sanji. He’s raising his voice too judging by the exclamation mark and you see, Zoro doesn’t usually yell when he’s cool-headed. But I don’t think he really thinks Sanji ‘stuck his nose in Big Mom’s business’ - that’s just Zoro being Zoro about Sanji and his way of showing that he’s annoyed but concerned about the cook.
And why is Zoro annoyed with Sanji? Note that Oda shows Zoro’s first reaction toward the story when Nami explains how Sanji left alone when he could’ve escaped with them. He doesn’t say anything but man, does he look dissatisfied. I believe that’s the main reason why Zoro’s so unhappy with Sanji - that he chose to leave his nakama when there could’ve been other options available (of course, Vito threatened Sanji with something but Zoro can’t approve of Sanji’s decision unless he knows exactly what that threat was).
Maybe it’s a bit of a stretch to compare Sanji to Robin in Water Seven&Enies Lobby arc since unlike Robin back then, Sanji has absolute faith in Luffy and did promise that he’d come back. But I think he’s still basically pulling a Robin by leaving alone without telling the reason in order to protect the crew… and we all know how that went down with Robin.
And maybe that’s what’s bothering Zoro - the fact that Sanji made the same choice as Robin when he had experienced the consequences of her decision just as fully as the others. Just like what Usopp tells Robin in the panel above, maybe Zoro also thinks Sanji should’ve put aside protecting the crew for once and told them about his problem first. After all, Brook did suggest to Sanji to wait for Luffy&co to arrive before making his decision.
Of course, even if Sanji listened to Brook it might not have changed anything because you know what Luffy’s like. But I don’t think Zoro’s pissed because he thinks they would’ve been in less danger had Sanji made a different choice. Imagine Sanji decided to wait for Luffy&co and told them about his past. After hearing his story Luffy gets pissed and decides to fight Big Mom. Would Zoro have blamed Sanji for deciding to wait for them instead of leaving alone? I don’t think so.
Another possibility is that Zoro feels somewhat betrayed by Sanji. I don’t think Zoro believes Sanji should’ve told them about his family because you know the Strawhats don’t give a damn about your past. None of the Strawhats blamed Robin for not telling them she was being chased by the World Government and I think the same can be said for Sanji, especially when he never expected his past to come back and bite him like this.
So that aside, I believe Zoro might have felt betrayed because Sanji’s always had his back in critical times so he never imagined the cook out of all people would become the source of the crew’s anxiety, especially at this juncture. He’s concerned alright and doesn’t really believe it’s Sanji’s fault but all this unexpectedness coming from none other than the shitty cook who he trusted the most is making him react harsher than necessary. Of course the rest of the crew also didn’t expect this from Sanji but unlike Zoro they don’t have a seemingly hateful relationship with him so they don’t need to act tough.
Maybe I’m being a bit impatient by trying to read Zoro’s mind when there’re many more chapters to go before we figure out what’s really up with him, but for now I think he’s not that adamant about not helping Sanji, though he is pissed with him. Remember when he stopped Luffy and the others from welcoming Usopp in Water Seven? He was so determined to make his point that he even took out Wado to show how utterly serious he was and even Nami cringed a bit at that. When Zoro’s dead set on something, not even Luffy can make him budge.
Here the atmosphere’s slightly different. Again Zoro’s in disagreement with Nami but the way they argue is almost like their regular bantering, not to mention that he doesn’t take out one of his swords to stop them going after Sanji. He does oppose Luffy’s suggestion but his face as he yells at his captain is almost comical. Although Zoro did insist they should focus on Kaidou, at the end of the day I don’t think he’d actively restrain Luffy from following Sanji – not because he lacks the capacity to persuade luffy, but because despite all logic deep down he grudgingly admits that’s the right thing to do.