In D2 it encouraged the opposite, actually. Basically you couldn't trust anyone, because they would ABSOLUTELY screw you over at some point. The drops were all shared, so when you killed a boss with a bunch of "friends", there's no telling if they would just grab everything and run off.
Also, to switch items between players, you had to get a trusted 3rd party to sit in a server for you to drop all your items, leave and come back with your other guy to pick them up. Too many times did this trusted friend "lose internet and drop from the server", losing all your items aka they stole it all.
It was pretty fun, actually. Mutual distrust and cynicism made interacting with other players pretty interesting.
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_foolmo_
'You are obviously intelligent and insightful' - Sir Chris about me