First, in most countries there is no law about diving, so you are allowed to dive without any course.
Also accidents are then covered in your insurance. Here it is the public health insurance.
So if people complaign about doing things outside of certification, the first question can be: Do I do anything that is not allowed by law? The answer is no then. So you do things right according to law.
End of discussion. I have done as open water diver deep dives during nighttime, dove in current and deeper than the 20m, etc, all on my own. Al advanced open water diver I started doing decompression diving. I also have taken as 3* diver new divers under water without being instructor. Of course some people complaigned, but I did nothing wrong according to any law.
All those dives where also covered by my insurance. And everybody can say in my country he or she is an instructor and found a dive agency. That is allowed, also as everybody is allowed to say he is a farrier, chiropractor, osteopath, sanio sacral practitioner, etc. In this case it can be important to ask where he did the courses.
BUT, of course there is a BUT, a BIG BUT:
Is it better to do such things with an experienced diver? Yes, so that is why some or most agencies state the first new dive of something must be done with an instructor. Or you need a cert to do things with a divingcenter.
Nightdiving is no rocketscience, but sometimes it feels better to do it with an experienced diver or instructor the first time. If an agency states the first dive must be with an instructor and you booked the dive with a divingcenter that is member of that agency, the divingcenter must follow this rule.
For some things some agencies don't have certs. A nightdiver cert is not available within CMAS Netherlands, nightdiving is part of a 2* cert, also driftdiving, deep diving, etc.
In the diving world you can say some certs are usefull or needed, some are maybe usefull and some are just for fun.
Usefull and needed, don't do it on your own:
open water, aow, nitrox, trimix, cave, ccr, etc
Maybe usefull, but also possible to learn on your own:
drysuit, nightdiving, driftdiving, sidemount, etc
(The theory about nitrox can also be learned on your own, but I think it is good to do some analysis during a course).
Just for fun:
biology, photography, boat diving, etc.
This list is not complete, but an example. Doing technical dives without courses is not a good idea. Cavediving as open water diver, a very bad idea.
But a lot of divecenters only prepare divers to be under water and holding by hand. The next step also need be done by holding a hand, and earn more and more money by selling the next course. There is no place for a diver who don't need guides, or learned things by being autodidactical. I want to see that divecenters are more open for divers who are really experienced enough and don't need babysitters. The guides are then there for the divers who need them or want them.
There is also a big difference in divers, some are naturals and some need more help. If you are one of the last group, don't worry, enjoy your diving and ask help.
If you think you can learn from a course and it feels better to take it, take it.