@Urouge:
Normally I'd assume you were trolling at this point, but I don't underestimate you. I'll spell this out for you. Every crew member will be willing to put their lives on the line for their friends when the situation turns ugly. In Caribou's shining moment, he pretended to be tied up while he watched his crew and brother drown. He clearly put his own life far ahead of his crew's.
To be fair, what could he have done? He's obviously not at the level of the monster trio to face the Kraken, and he knows that. He's also a devil fruit user who couldn't have gotten even close enough without sinking like a hammer. We've seen so far that stupid as he is he will think of what the best options are, and dying in order to save his crew who'll die anyways can be considered a great waste.
That aside, there is no argument he's a selfish bastard seeing how he recovered pretty quickly from the fact that his crew AND brother got destroyed because they were trying to save him. Seriously, Moriah can be considered evil and take a look at how he processed losing his entire crew. Meanwhile, Caribou is unaffected.
@Reyairia:
Stealing 2 million worth of their money, despite knowing that they wanted to use it to fix their beloved ship and beating up one of their crewmembers isn't exactly great behavior either, to be fair.
Um, many of the crew members in the past have done shitty things with the mentality that hurting pirates is ok because they're pirates. Bounty Hunter Zoro? Pirate-hater Nami? Baroque Works Robin? Sanji probably beat up a lot of them in the Baratie as well. It's the risks that come with flying a pirate flag, the law doesn't apply to you, so people can justify doing shitty stuff like that, especially if you're getting the money to fuel your dreams and the dreams of a group of people the rest of society gave up on. You cannot compare what Franky was doing to what caribou is up to.
@Louis:
All that would be completely valid if only he wasn't a psychopath who buries people alive for kicks. Well damn, he would have been so cool if not for that! Like a second malice filled Ussop, or a Sanji who wouldn't just peak! What fun!
This is the main point people forget. He may be having good interactions, may be interesting, and you could make up a purpose for him, but goddamit he's a deranged lunatic who FOR NOW has no redeeming qualities and as such deserves no consideration.
Now, can Oda redeem his character? sure, why not. But before he does so there's really no reason to think that Luffy will want a murdering lunatic in his crew of happy-go-lucky dream-following pirates.