To me, it's kind of like taking all the college classes needed for an Associates Degree, for example, then deciding that you don't need the degree for a job, and the degree itself isn't a class that teaches you anything new, and that since applying for and getting the degree might cost a fee (don't know offhand whether it does, but for this example let's say it's a $50 fee), you don't need it.
It's very different from that actually. To use your comparison, PADI MSD is more like having the option to take 60 elective credits in whatever fun subjects you want, neglecting things like English 101, History, Algebra, Biology, etc. and then applying for an Associates degree.
Accredited institutions require those core subjects because they are important to a well-rounded and college-educated student. By awarding an Associates degree they are showing that you have learned core and important information. What would be the point of college degrees if they had no foundation in important and critical subject areas and only allowed someone to take fun and useless courses for two years?
Is it really fair that while one diver takes rescue, buoyancy, deep, navigation, night and search/recovery to earn MSD another diver can take rescue, naturalist, photography, Nat. Geo. diver, shark diver, and Fish ID to earn MSD? Which one of these divers is truly closer to being a Master Scuba Diver?
Any MSD program offered by an agency that doesn't have an actual course involved and only is awarded because of a minimum number of plastic cards should be called "Experienced Diver" at most and certainly not "Master Scuba Diver".