God Being Just Because His Creation Loves Justice
And also- if there is the possibility that the aql God gave us is actually misleading and flawed then we would actually not be able to establish he is qaim bil qist. In this situation us humans are helpless. But then the possibility of the situation is the problem- because as Ghamidi sahab mentioned- if we didn’t believe that God was established in justice- or if we even have an inkling of doubt in that attribute- our whole faith in him is destroyed
Some forethoughts: If God created this universe snd he was being oppressed by being made to deceive us then how could this universe remain standing?