@Jabra:
How could they?
Judging from Jinbe's talk with Neptune, he wants to leave Big Mum's crew without causing harm (to the Island or his crew). Bringing Luffy along who just declared war on her would… contradict that.
Well they're going to fight her anyway so…
--- Update From New Post Merge ---
@Noqanky:
How are people still discussing Jinbe? It's extremely obvious the crew wants him and that Jinbe wants to join as well upon Big Mom's ties being broken. EXTREMELY. At this point it's more of "I like him" and "I don't like him", neither of which are good arguments for him joining or not.
Seriously, if you think he won't join, suck it up and realize that the signs point to yes (even though I do admit it's not entirely confirmed yet.) It would only be an extraordinary situation that would lead to him not joining. It's that overwhelming.
Negates all sureness of him joining. Look a Vivi look and Bon Clay. We can make excuses "she had a country to run" and what not but as in Drum island kings can be replaced. And what of Jinbe's crew? Also not to long ago people (meaning everyone I heard talking about this series, I'm not making this up hit up Youtube or the One piece Podcast ) said that after the volume cover, and after the blood donation, and after Luffy saying "Join my crew" that Jinbe was going to join but did he? No. That's why every time I hear these detailed explanations as to he's going to join later I pass them off because I think of the Brook situation (If you read this series I shouldn't have to explain what his situation was). To me this situation and that one are near identical. But then again people made baseless Zoan theories on someone who just told them what fox fire meant/was.
Also I like to bring up colors and themes a lot and here they're written off as baseless, frivolous banter. However I have to wonder why in the world would anyone who has made a group of characters who are designed in such a way that no one Straw pirate remotely resembles the others, and if anyone pays attention Oda like Akira with Dragonball makes a lot of his female characters look relatively the same, however do Robin and Nami look the same? No. Do they have the same themes? No. We can all say "Well Jinbe is a big blue Goomba how does he look like the other characters on the crew?" Well, like you I can she he is a Fishman but I also see that he is a Japanese characters "WELL AREN"T ALL THE CHARCATERS JAPANESE THEY COME FROM JAPAN!!!!" Yes I understand where they come from however some characters have really blatant themes that would either go with another country besides Japan. For example Jinbe and Zoro both where kimonos have attacks that have Japanese puns Jinbe is design is very similar to a Oni, Zoro asura comes from Hinduism and Buddhism, very popular religions I Japan, Zoro comes from a kendo dojo while Jinbe comes from a Fishman island which is undeniably Japanese in theme.