To what extent is that perhaps just a learnt behaviour, though? Maybe it doesn't actually serve any true purpose, it just started, and it's continued as an institutional habit, passed from veteran to recruit.So @Gethsemani, there's an anecdote to counter your claim. But both can be true. They can be both tight-knit and rough with each-other.
I agree with Gethsemani's claim that I think hazings, and all sorts of extreme toughness are actually attempts to break people down so they can be remodelled. But of course if they are being remodelled, the model they've been built around originated from emotional and physical hardship. So perhaps that stuff simply becomes the new thing to bond around. It doesn't have to be that way, and it doesn't make them any better at their jobs. It's basically just what they were taught to be.