There are three main reasons we have people with non BSAC qualification:
1 - they did an OW course abroad and totally loved it, came back to the UK and wanted more diving.
2 - they did an OW course abroad and were scared that they actually had no idea and wanted reassurance and further training, including sometimes them insisting they start again.
3 - they need particular timing or a want a particular instructor so take a course with whoever suits.
I think that the old fashioned approach is actually the one taken by the big commercial agencies. By categorising deco diving as completely 'other' and having stuff like having to not dive for a period of time if a diver goes past NDL they have created a whole new category of pushing things. Having hard rules rather than having divers evaluate risk.
That is understandable though, given that their business is 'pile them high and sell them cheap'.
Regarding your 'enabling' clubs to sit in a bunker - taking Nitrox as an example. Nitrox has been on the OW equivalent course since 2007 (at least). No extra courses required.
Diving qualifications do not stop anyone from doing anything. Diving courses should educate people so they can make informed choices. To get a 50m air qualification with BSAC you need to have done Ocean Dive, Sport Diver and Dive Leader. Each of those REQUIRES a number of experience dives and then Sport Diver and Dive REQUIRE post qualification depth extension dives. This means that anyone qualified to 50m MUST have had at least 6 dives (with a Nationally Qualified Instructor - not an assistant or club instructor) just to extend depth. This is on top of those involved with the lessons and the other experience dives (i.e. nonlesson dives to expand on diver experience of different conditions - so 20 dives in a quarry is no use). By the time they have done all this an enthusiastic Dive Leader will most likely have been diving for two or three years and have a 100 dives. By that stage they ought to be able to understand the need for redundancy, helium and so forth and so be making INFORMED choices.
If I were look back at earlier qualification schemes and manuals within BSAC I think (my manuals are 3000 miles away) that in the 70s and 80s a Third Class Diver, the then entry level and equivalent to Sports Diver, had a recommended limit of 50m, although it might have been 60m using the RN tables. It took about 20 dives to get to be 3rd class, but of course you knew your place in the pecking order.
So clearly, nothing has changed since the 50s.
Like combating underage sex or drugs with 'Just Say No' is bound to fail, telling people they have hard limits will fail. It isn't better to give people the tools and experience to decide for themselves.
If you want to see how that works out go Scapa Flow and count the single cylinder divers. There will certainly be none without a pony and probably none at all. If fact on some trips now there will be no OC divers at all.
If we want to consider modern practice, should we not think about whether people should be doing big OC dives?
TDI Advanced Trimix OC? They must be stuck in the 90s!