Why bad people can't be good friends

Must the best friends necessarily be good people? On the one hand, as Aristotle puts it, 'people think that the same people are good and also friends'. But on the other hand, friendship sometimes seems to require that one behave badly. For example, a normally honest person might lie to corroborate a friend's story. What I will call closeness, which I take to include sensitivity to friends' subjective values and concerns as well as an inclination to take their subjective interests as reasons for action, is characteristic of friendship. But this seems to require that good friends should be morally flexible, more so than is compatible with a virtuous character. This would imply tension between ideals of friendship and ideals of character. But there is an important connection between virtue and friendship which arises precisely from friends' closeness, when concern for wellbeing, another important feature of friendship, is also taken into account. This helps mitigate the tension and shows how friendship and virtue are interconnected. The connection in turn provides friendship-based reason to think the best friends must be good people, even though concerns of friendship may occasionally clash with other moral concerns.