Either a) your opponent truly does believe that you've disabled your steering, in which case the outcomes are identical and the actions are equally rational, or b) we account for the (small?) chance that your opponent can determine that you actually have not disabled your steering, in which case he ostentatiously disables his and wins. Only by setting up what is in effect a doomsday device can you ensure that he will not be tempted to information-gathering brinksmanship.