This is just a way to emphasize the starting postulate, a way to say that the hypothetical situation is a given, maybe to avoid someone questioning that before even considering the asked choice. However, in its general meaning it is indeed a simple assertion, extremely close in sense to the variant you quoted at the end of your question, which could definitely be used and would probably sound just as good.

But I guess it’s the same for some uses of to have to or must. What whould you think of the ‘duty’ meaning in the following example ?

If you had to be either a klingon or a borg, what would you choose ?