Not everything is so black and white, IF an aircraft has a toilet U/S for instance, it IS a defect so technically any Pilots flying that aircraft ARE flying a "defective" aircraft, but obvious safety is not compromised.
It ONLY ever becomes a problem if Pilots push the limits of the MELs in order to get home on time, there must be some commonsense involved here.
I have seen this all my 40 years in the Industry, and have even done this myself, I helped Pilots ferry (no pax) an F27 aircraft from Australia to England years ago, a trip of some 10 days and not one defect in the log books until we were on finals into Norwich when I wrote up 3 pages of defects.
By the way, everywhere I have ever worked the Captain can always over ride an MEL and refuse to take the aircraft, but he must have a VERY good reason and be prepared to explain his reason to the chief Pilot and Company.