Whereas with Fiat, no one can differentiate them. You can literally be given money paid as ransom by the bank and you will never be aware this ever occurred including the banks themselves.
What we see now in Nigeria is massive corruption in the government, the government has a way of tracking every cash line specially given to anybody. In the early days of bank robbery, I have witnessed people arrested because money stolen from bank safe which the serial number ranges were documented were seen in their possession and investigation ensured until the real criminals were apprehended.
Fast forward to the recent case of kidnapping, if the government and banks wanted to cooperate with individuals, they can give the specific set of cash to them for ransom and alert the police to begin tracking the distribution of that money, but what we see here is a compromised government, responsible for the insecurity, so those expertise are swept under the carpet.
I believe every governments know the truth but looking for a way to suppress bitcoin growth or have a free share of it for themselves.
I don't like the idea of tainted bitcoin. It makes it look as though some bitcoin are worth more than the others and it is a government control tool to limit the use of cryptocurrency and of course track coins acquired from illicit activities. The only problem is that even innocent people end up victimized if they receive the coins for legal anonymous payments.
Good thing the taint is in its tx history, there are some features like CoinJoin and services like mixers that can help alter its history and make the assumed taint harder to figure out.