Well, that just confuses me. If anything, its more like "I think no one wants to spy on me so I will set my threat level to low", which is what happens according to the bonuses of -0 happiness and 75% counter spy readiness. The flip side is "I think someone is spying on me, I will raise my threat level to severe", where you get -2 happiness and 125% counter spy readiness. The lower threat levels don't mean you will get spied on less, just that you will be less prepared if someone does spy on you. The opposite applies for the higher threat levels.