Now that you have clarified, I wish I could downvote a second time.
Tit-for-tat is a good strategy in the iterated prisoner's dilemma regardless of whether the players are human and regardless of whether the other player is "on your side". In fact, it is pretty much taken for granted that there are no sides in the PD. Dre was downvoted by me for a complete misunderstanding of how Tit-for-tat relates to "sides". You were downvoted for continuing the confusion.
Oh, you're right- my response would have made sense talking about players in a one-shot PD with communication beforehand, but it's a non sequitur to Dre's mistaken comment. Don't know how I missed that.
A monthly thread for posting rationality-related quotes you've seen recently (or had stored in your quotesfile for ages).