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.
This the kind of trade-off we have to live with if we are to continue to use bitcoins on a daily basis. Hackers will be paid in bitcoins. Untraceable and clean. But this does not justify that bitcoins are evil and will be used for that matter. It is only a medium for trade like foat money.