There are many people who believe bitcoin is the perfect solution for black market trade, tax evasion, and other frowned upon activities. Cryptocurrencies seem to be working well with these types of exchanges as darknet markets, gambling sites, and sex workers are using bitcoin for their operations. The reason bitcoin is so appealing to these kinds of markets is because bitcoin is censorship resistant and allows the end user to decide how their wealth is spent.
Fiat is still far ahead, the millionaires who finance wars in other countries, who commit crimes against humanity use fiat.
Crimes involving bitcoin do not outnumber fiat.
However, there are a bunch of people who believe these types of unfavorable activities taint bitcoin’s image.
Diamond and gold are stained with blood... how many barbarous crimes have already been committed involving precious stones.
Anything that someone creates/invents will be misused by some people.
Take as an example the knife: the people instead of cutting the food? Use the knife to take life from others