If you tell me that "should" has a usage which is unrelated to "right", "good", and "ought", then that usage could be adapted for aliens.

One of the standard usages is "doing this will most enhance your utility". As in "you should kill that motherf@#$%". This is distinct from 'right' and 'good' although 'ought' is used in the same way, albeit less frequently. It is advice, rather than exhortation.