An MEL has to be considered in the context of multiple factors...other Mx items, Wx, etc.

Sometimes an legally MELed item might be a no-go in reality, ex. FMS MEL for a short, low-alt leg in complex airspace with a non-prec approach into an uncontrolled field at night in a blizzard. We are just not that proficient at raw data.

But honestly, in the case of the pax door on a CRJ: Very simple MEL, very simple work-around. Communicate the issue to ramp and FA so they know not to drop the door. I don't agree with the need to cancel the flight over that...rampers do a dangerous job every day, following proper procedures to avoid being injured by equipment should not be anything new to them.

If the door DID get dropped, yeah I would need Mx to check it out before flight.