This is pretty obvious, but I never quite thought of it in those terms: The prisoners' dilemma shows the need for the virtue of trust (or faith, in a non-theological sense). In the absence of contrary evidence, we should assume others to act well, to cooperate.
This assumption perhaps cannot be justified epistemically non-circularly, at least not without adverting to theism, since too much of our knowledge rests on the testimony of others, and hence is justified by trust. Our own observations simply are not sufficient to tell us that others are trustworthy. There is too much of a chance that people are betraying us behind our backs, and it is only by relying on theism, the testimony of others, or directly on trust, that we can conclude that this is not so.
It seems to me that the only way out of the circle of trust would be an argument for the existence of a perfect being (or for some similar thesis, like axiarchism) that does not depend on trust, so that I can then conclude that people created by a perfect being are likely to be trustworthy. But perhaps every argument rests on trust, if only a trust in our own faculties?