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.
I completely agree with you, it is not the creation of bitcoin, it is the people who are so selfish that they will do anything just for the money. Bitcoin has nothing to do with the dirty works of men, it is just used by the greedy people to scam and fraud other people for their own benefit.