In Scotland in the early 2000s, there was a moral panic over a tonic wine called Buckfast, made in Buckfast Abbey by an order of Benedictine monks.
It's the kind of thing meant for your granny to have when sick. It contains caffeine and alcohol, and neds started drinking it because caffeine and alcohol both feel good (humans have known this for thousands of years).
It quickly became part of the local youth culture, and was quickly blamed for all the deep-seated anti-social behaviour issues prevalent in the region. It was known as 'wreck the hoose juice'. Breathless tabloid headlines were written, schlocky documentaries were made (I was made to watch one in school), and politicians started laying the blame at supermarkets for selling the stuff.
The big supermarkets stopped selling it of their own accord, and still don't to this day. They were hurt by the bad PR and like to get ahead of regulation, which is not toothless in the UK. Buckie, with it's now notorious reputation, started to be drank by artsy pretentious students instead of violent neds. And would you believe it, when it was drank by this different demographic, the problems magically disappeared!
My point being, observational studies are useless here because only a certain kind of person is consuming a drink called 'FCKED UP'. Caffeine is one of the most well-studied drugs in medicine, and we know it's safe. Evidence to the contrary would have to be strong, not be anecdotal or observational.