"You only defect if the expected utility of doing so outweighs the expected utility of the entire community to your future plans." These aren't the two options available, though: you'd take into account the risk of other people defecting and thus reducing the expected utility of the entire community by an appreciable amount. Your argument only works if you can trust everyone else not to defect, too - in a homogenous community of Briennes, for instance. In a heterogenous community, whatever spooky coordination your clones would use won't work, and cooperation is a much less desirable option.