...nonono, passive scores shouldn't be automatic success or failure: you invert the roll...

...say you want to know whether a party detects traps as they prowl through the dungeon: you subtract twelve from the trap DC, use that as its modifier, and add it to a secret D20 roll which you compare with everyone's passive perception to determine whether the trap successfully avoids detection...

...as long as you properly account for all applicable modifiers, you can do the same thing for any secret ability check or saving throw, or for a single roll to circumvent the party dogpiling a group check...