A lot of the talk about betrayal hinges on the premise that it is "more logical" to not want to split the pot and keep it all for yourself. Now, we can debate the logic of that premise at length but a central problem of economics is that it's not completely logical, or rather it's an attempt to apply logical models to systems of behaviour that sometimes veer into irrational territory. Caleb has already mentioned this in discussions about things like the Tulip Craze, how an entire nation based ruined its own economy in the name of some pretty flowers with no use or intrinsic value.
Let's then move on to the "betray, run, keep all the loot for yourself" - that only holds up under some very specific, hopeful circumstances. First and foremost, you better be absolutely sure those other guys who worked for the money are dead, because they're going to want the profit of their labour and a few pounds of your flesh in interest if not. So, you know, headshots are handy. You also don't want to get a reputation as a betrayer - otherwise good luck getting work again, or finding other people willing to form a Taker crew with you - and in a setting with Ubiq and Lifelines, even one survivor of your last Taker party who can, say, post footage of you, say, shooting your friends and running with the loot, that just made the trek through the Loss to the Recession a bit longer and a bit harder. If your money isn't enough to buy your way out of the Loss, and your name is out there as "that murderer who murdered all those people (you know, his murder victims)", you're going to get treated like a Raider, not a Taker. Remember, being reliable is a positive quality, not a negative one, when it comes to negotiations on both sides - you want someone who you know will pay you and they want someone they know will get the job done.
Let's return to the fundamental problem here of "should people backstab each other in survival situations"? It's a fundamental tension within capitalist economies - you want to rip other people off for your own profit - and philosophy. This is literally just The Prisoner's Dilemma - in a situation where it is "logically sound" that to betray someone is more profitable than co-operating with them, no-one can be rationally expected to co-operate with anyone, ever. Ripping off everyone is not sustainable unless you have a monopoly on what you're using to rip people off. And no-one wants to be ripped off themselves. This is where the social contract (for want of a better term) comes in. Namely, "I won't screw you if you won't screw me - or at least let's find sustainable ways of mutually screwing each other". And, of course, this is where literal contracts come in so that agreements are made, can't be changed and have some form of exchange. Look at The Reformers, how they early on fleshed out a social contract for how loot would be divided up between them. None of them have gone hungry over the course of the game so far, and even with the miscalculation of the last job's loot they were well in the black. If your group takes a different approach - say, "keep what you kill", your only profit being what you can physically take - and in the absence a formal legal system then yes, there's no reason why you shouldn't backstab the other Takers in that group. But there's also no reason why they shouldn't backstab you - so try and do it first. That's the thing about contracts - they provide you with protections and rights as well as the obligations and covenants, so they're very valuable.
And don't forget, no person is an island. You need other people. That means giving to them, but it also means receiving from them, which is an inherent part of the setting and the system - you provide to your Dependents and in return are healed of Stress. We're a social species, no one individual is capable of total self-sustainment and thus must (or should) act in a somewhat-social fashion in order to receive the benefits of participating in a wider society. I hate paying tax, but I love the NHS so I put up with a little garnish from my pay to know that if my liver decides to die I can get that sorted out. So, if a backstab is going to come it's probably going to be in a MR JOLS job - where the payoff may well be enough to offset the risk inherent in, you know, murdering all your friends and departing from civil society.
Just think we give David shit for dropping that kid.
You know what I realised listening to the recent Delta Green episodes? David killed a Dark Young.
A Dark YOUNG.
Even when he's killing monsters,
he's killing children.(Also, the criticism there wasn't that he killed the kid so much as that it was unnecessary because Ross had wrestled him and gotten control of the weapon, so Malleus wasn't in danger and they were literally right on the edge of escape when POP POP. But David being David, he's never going to admit to it. The Indigo Infanticide strikes again!)