You could call that pessimistic, neagtive, narrowminded, underestimating (what is the opposite of naive..naive is when you wrongly believe everything is great pure honest and innocent, but what if you wrongly believe everbody has ill intentions, everything is rigged, noone can be that smart etc etc, everything s a fake or fraud in your mind)>
Conspiracy theorist? paranoid? I have a tougher time coming up with these words than I thought, even if it is not in my own language, I thought I could describe it better haha.
Cynic, I guess that comes closest :)