The third choice you gave in the prisoner's dilemma breaks the game itself, and so is invalid (they can also fly away on the private jet of a friend of theirs who infiltrated the prison camp and managed to conceal the jet among the trees, and infinite other possibilities). This is a game, and not real life. The beauty (or ugliness) is that most real life decisions can be reduced to somewhere along the Nash equilibrium scale, depending on the amount of trust. Even escaping prison can be evaluated along the scale.
A and B are in Nash equilibrium if A is making the choice given that B will attempt to secure the most overall beneficial choice solely
for B him/herself, with no trust in A (which is in many cases the worst choice B can make from A's point of view). And vice versa. Nash equilibrium is reached when all trusts vanishes. The first paragraph in the Wikipedia article summarizes the equilibrium nicely.
Therefore, the example in your first post about dating is the exact opposite
of Nash equilibrium, which I like to call Nash anti-equilibrium. Yes that solution is the best for the group, but it is also the most unstable. Anyone
in that group can have gains by changing their strategy (going for the main girl). Either there is a context issue on that quotation, or someone didn't do enough research while writing the script
Nash equilibrium is not a good thing. In its purest form it completely disintegrates any social bond and trust. And the result is in the worst interests of the group itself. In quite a direct sense, Nash equilibrium is almost exactly like cancer.
In any case, I agree that in most cases Nash equilibrium cannot be united with the most optimal action of the group as a whole. By the way, my sentence that you quoted was not directed at the UE/IMSLP dispute per se, but a more general comment.