All bad things that can be done using BTC and with other cryptocurrencies are being done for centuries using Fiat currencies. Let's accept the fact that human nature is good as well as bad, there are many people who are doing things for the welfare of humanity using cryptocurrencies. It's not fair to say that BTC can only be used at the dark web and has only negative use cases.
Every invention is a vehicle and is being run by humans. Take the example of guns, for instance, they can be used to defend yourself and also to kill innocent people but that doesn't make guns accountable for their bad usage. Same holds true for BTC and all other cryptocurrencies