A lot people use fiat for crime and gambling too.
Bitcoin might be not the best in terms of privacy, but at least it's the best coin for investment and privacy at the same time. The number of asset that the price appreciate and can protect your privacy is low, most of the time you can only pick one.
I really despise this argument; fiat currencies have always been used for crime activities, yet people still blame Bitcoin and cryptocurrencies. I'm not saying that they aren't used in the dark web markets or for money laundering in mixers, but that's simply the tip of the iceberg. Most transactions are still conducted with fiat currencies, and those who were involved in such activities always found ways around the law. Cryptocurrencies weren't a thing until the early 2010's, yet people focus on the negative aspects of a few darknet markets in a timeframe of less than 15 years.