Anything can be used for illegal activities.
I think that the main reason why btc has been rejected by society is that there's still much to learn about it and it's easier for them to speak ill of it than to try and deal with it.
I agree with you. Fiat has been you for many illegal activities for over centuries and no one actually wants to reject it. As long as bitcoin keep developing, no one can ban it or even ignore it.
I think all the currency that has the price will always be used for any illegal transaction currency, if that is possible may be used, including the bitcoin ?