Is recreational divers obtaining divemaster certification a common thing? Is becoming a divemaster too easy? Does being a 'professional' diver have less meaning than other industries?
I don't know if it is 'a common thing'. I do see many people, who are passionate about diving, considering becoming a DM because they can then work at what they love doing (even if not making a living doing so). I don't think that the process of becoming a divemaster is necessarily 'too easy'. And, I don't think that being a 'professional diver' necessarily has less meaning that being a professional bricklayer.
Being a professional' can merely mean getting paid for doing whatever you do - a 'professional basketball player', a 'professional auto mechanic', etc. And, if that is all that being a dive professional means, then diving is in just as sorry a state as professional sports. But, I read the other thread and I see where the critics of the OP are coming from. Being a 'professional' also seems to be related to the concept of professionalism, which is characterized by many attributes, prominent among which is 'doing what is right'. I know of many people who hold a professional credential, who may not earn their living practicing that profession, but who consistently adhere to the principle of 'doing what is right' (whether I agree with them, about what is right, or not). That is, to me, what being a professional is very much about.
When I was in my early health professional career, I decided to go to law school. I did not necessarily want to be a practicing lawyer, rather I wanted the intellectual training, the way of thinking, the approach to analyzing a problem that I perceived to be part of the law school curriculum. Although accepted to a prominent school, I did not enroll, because of a family illness that came up after my acceptance. I would still like to do that today, and now have the time as a retired person, although not quite the same passion and energy I once had for spending 3 years of my life in that pursuit. But, whether I ever practice law or not, generate any income from it or not, I suspect I would adhere to the ethics of being a legal professional - 'doing what is right'.
I would hope that anyone who pursues the DM credential would do the same, whether they worked as a DM or not. They would do what they believed to be right. I am less concerned with how much money they make at being a DM, and frankly less concerned with their absolute skill, as with their mentality. I would hope that, if they observed behavior that was not consistent with accepted practice standards, ethical principles, or regulations, that they would point that behavior out to civilian, governmental / regulatory, or professional licensing / certification authorities, and the public, as appropriate.