While the rightful purpose (or lack thereof) of the Master Diver cert. in the PADI system continues to be a hot point of controversy, I think the following points have some merit.
It is:
1.) An offering that encourages divers in the early stages of their hobby to keep getting more training than they otherwise might (such as Rescue Diver, which is a good course but some might steer clear of thinking it's just for people who want to be amateur scuba lifeguards), and therefore likely makes some people better divers earlier than they otherwise would've become.
2.) It does encourage people to spend more money on PADI offerings, including the card. PADI is a business. They seek to make money, in addition to whatever other goals they have.
It is not:
1.) The pinnacle in non-professional diver training.
2.) Under the PADI, a separate course with additional knowledge & skill development.
3.) Proof that a diver is an excellent overall diver.
4.) A title created to honor some rare few 'world class master of the craft' divers by being so exclusive as to be irrelevant to the large majority of hobbyist divers.
We've had some discussions about what a true 'master diver' is. Is it a cave diver who can wedge through tight spaces with amazing buoyancy and without stirring up silt? Is it a world record deep diver with amazing resistance to narcosis? A technical diver who can execute amazingly complex dives with a wide array of equipment?
In the PADI system, it means you completed AOW, Rescue Diver & 5 PADI specialties and at least 50 logged dives, then paid $40 or $50 or whatever for the card, which lists your specialties on the one card.
If I ever get all that done, I'll probably get the card. But as you can see, views vary widely.
Richard.