Science is built upon repeatable experiments that can be used to test hypotheses. It is not built on axioms and logical extrapolation- those are used to form new hypotheses but they are insufficient by themselves. We don’t decide something exists, we hypothesize that it exists and make predictions based on that hypothesis. If experimental results line up with our predictions then we call that a theory. If new data contradicts the theory or hypothesis then we revise and try again.
Or the borg achieving time travel tech was an inevitability and Janeway destroying them was a necessity to keep the borg from assimilating all life in a manner similar to First Contact (thus negating the existence of the temporal police).