He didn't,
It just sounds like he didn't want to be involved in something so plainly dangerous. Captains aren't immune from bad decision making just because they are captains. If you ask me it sounds like Flap43 used good CRM to possibly prevent a nasty situation from developing. Remember, flight safety is a team effort and sometimes us captains need saving from ourselves.
You don't need to be an airline pilot to know that certain bits missing/ U.S. on an aircraft means it is a no-go. Even the MEL states that obvious items required for despatch, like wings and wheels don't get an entry in the MEL.
I would be questioning the judgement of that captain (whichever airline he flys for).
Flap43, you can inform me of any defect you suspect on the ramp at Manchester and I will gladly listen. Keep up the good work.
PP