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 ?
Bitcoin was already used for illegal activities from the start because is hard to track transaction, but not only that, many peoples using bitcoin because easier and cheap fee transaction than bank, so bitcoin can be used for everything even for illegal transaction.
Although bitcoin was already used for illegal actvities, but bitcoin was used for good thing too. Fiat and bitcoin is the same, both are currency. The users are determine what their currency for. We do not have to concern with illegal or legal but we better concern in bitcoin dissemination.