Encrypt all the things!

There's no contradiction, nor even a tension. We can co-operate perfectly well without agreeing on everything, or even most things. Much of the poisonous journalism about the Occupy movement has pivoted on this fallacy, accusing them of not having a vision, as if they were a political party (as if any of the political parties had a vision anyway).

Anarchism means "without rulers", not without rules I suppose.

So yes, if one posited a society of people who would generate rules by consensus, and then abide by them, then a cooperative would work.

My impression of anarchists is that they don't want any rules, either implicit or explicit, which would not bode well for a cooperative society I would suggest- concepts such as ownership of ones own labours and so forth being fairly important.