I wouldn't doubt people who have used bitcoin for years, but what if:
If bitcoin had been legalized worldwide but with policies like Elsalvador (under control), then not everyone could not identify real and fake bitcoins because they were not introduced to how to transact bitcoin onchain. In fact bitcoin addresses can accept some bitcoin forks. If one day a scammer builds a phishing tx explorer site and designs the interface as if it belonged to real bitcoin's blockchain, the victims are unaware because of their ignorance.

Perhaps the OP's question is irrefutable for some reason. And what makes me believe that bitcoin can be "counterfeited" is that there are cases of wrong deposits on CEX, which BCH they thought was BTC.