And it is probably not nice for the pilot to fly with to many MELs.
But as a pilot, do you think there are flights where the plane should have repaired before departure. And do pilots have the courage to say NO to a flight, only with suspicion to a fault.
You can also have temporary failures which are hard to find, and not pressent by mechanics troubleshooting.
What is "nice" isn't relevant. Only what's safe, and what's legal.
The purpose of a Minimum Equipment List, and a Configuration Deviation List is to spell out exactly what can be flown in an inoperative condition, the circumstances under which it may be done, and the duration for which this can be done, safely. Further, the MEL/CDL serves to make the aircraft legal and in compliance with approved data.
Why should a pilot say "no" to a legal, and safe flight?
If a "temporary failure" is hard to detect, then what exactly is the point? Are you referring to "could not duplicate?" If the problem is intermittant, then there's only so much that can be done to find it.
If airplanes are being flown with inoperative equiment which is legally deactivated, and for which legal provisions have been set forth allowing for the safe operation of the aircraft...there should be no objections to flying the airplane.