I think you need to do your research and some are appropriate for some people. I am on a few , mostly due to gastric bypass surgery. I think the vitamins would be useful to most depending upon deit. B,C and D are needed by many. On the other hand people who have a virtual closet full are wasting their money but maybe the placebo effect ( something so real it has to be taken into account in drug trial) is worth it to them?
BTW, being that this board is largely populated by men you picked a really poor example of what "dangerous" supplements might have in them. LOL
For an example Kratom which can help fight pain and possibly assist with opiod withdrawal and has a buzz level if you want to take enough with much less danger than is associated with opiates .Yet the government keeps trying to ban it but keeps getting shot down as there is no evidence that it is dangerous enough to ban.