I have seen some news regarding hackers, terrorists, and other criminals using bitcoin for illegal trades.
How the police can find about these transactions?
Even if is hard to track illegal transactions, I don't think that Bitcoin can be a danger to society, since the problem is the society and its people.
Since the beginning of the internet this is happening ( the bad people committing crimes) and no one is willing to shutdown internet because of that, so in that matters Bitcoin should be equivalent. I think those illegal transaction are one of the reasons some governments and the media are trying to depreciate bitcoin, but the problem is not Crypto/blockchain or Bitcoin, is just the society.
Bitcoin does not have any role in the criminal activities. There was criminal activities before bitcoin's formation. It is not easy to track illegal transactions, but I didn't think that bitcoin will do harmful to the society. Criminals are using bitcoin as medium of exchange. Media and government is against bitcoins, because they have no role in determining the price level of bitcoin. Supreme authority of bitcoin is vested with its users.