Yeah, I guess that's why I couldn't really
come down on one side or the other; I started to write an argument for one side, then switched and wrote an argument for the other, then finally decided that this came down to whether you wanted to go strictly by the text (in which case you can choose an opponent who couldn't take control of a site) or go with what Decipher probably intended (in which case you can't). The problem ultimately comes down to to fact that Decipher just messed up a little on this card, and do we want to do what it says or what Decipher meant?
And, Chompers, as Elessar's Socks just said, you do have to choose an action that is capable of being completed; the problem here is that the second option ("choose an opponent who may take control of a site") is probably satisfied as soon as the FP player chooses an opponent, regardless of what that opponent can do.