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.
Criminals will always be anywhere you go, even in churches there are criminals in our government and we cannot stop them instantly because every people have their own freedom of mind they can do whatever they wanted even if that is bad. And in this case of course bad people also can adapt in the new happenings in the world. They van know access bitcoins too and some.of them are using them because that is untraceable. So if you ever known a people who are doing it just stay away and do not be a part of those people who ruined the name of the bitcoin