There’s a dilemma or a paradox here only if both agents are perfectly rational intelligences. In the case of humans vs aliens, the logical choice would be “cooperate on the first round, and on succeeding rounds do whatever its opponent did last time”. The risk of losing the first round (1 million people lost) is worth taking because of the extra 98-99 million people you can potentially save if the other side also cooperates.
There’s a dilemma or a paradox here only if both agents are perfectly rational intelligences. In the case of humans vs aliens, the logical choice would be “cooperate on the first round, and on succeeding rounds do whatever its opponent did last time”. The risk of losing the first round (1 million people lost) is worth taking because of the extra 98-99 million people you can potentially save if the other side also cooperates.