He is a blood thirsty murderer…people like him don't just change......and he isn't the type of person they'd want on their crew.
Also God dammnit...stupid breaks....why does he do this to us??? Was the fact we had a 1 mon th torturous break not enuff?
This is a fair point. Let me explain why I think he will change.
1. Crocodile (his actions speak louder than his words).
2. Flying Fish Riders. These guys were slavers and EXTREMELY evil, selling people into bondage for slavery. Would you agree that they 'changed'?
3. Luffy's ability to make anyone his ally, according to a statement by one of the strongest characters in the manga.
4. Who was the dude on the chopper island, the evil king? He changed.
5. I'm sure others can name characters who started out bad and turned good because of luffy, this has happened multiple times in the series.
Cariboo is the ULTIMATE example, because he is sooooo evil right now. That's exactly why he is perfect for the theme of "redemption."
He will go from evil to good, and be redeemed. Until this happens he is an enemy of the strawhats, but always remember that Franky robbed the strawhats in their time of need, and then his group beat the living hell out of Usopp, then he fought against Luffy 1v1 in a very tough fight, etc.
The fact that he is traveling with the strawhats from mega arc to mega arc is huge and it is a first time in the entire manga that a non strawhat has done so.
The scene with the krakken (ugly appearance, mythically evil to sailors) is a parallel to what Cariboo represents.
When Luffy says he is going to "tame" the Krakken, this is really a foreshadowing event that he is going to "tame" the Cariboo. This is why Cariboo's reaction is specifically shown.
"How could something that evil/monstrous be tamed" is the point of it. The immediate reaction to Cariboo is also, "how could something that evil/monsterous be tamed."
Now, I can't say for sure that he will join (of course), but I predict that he will and even if he doesn't join he will be significantly changed for the better by the strawhat crew, and will probably at least end up as a friend.