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.
For sure, no one would be able to ban bitcoin because it is does not belong to any government, country, race or set of people so if you think of banning it you are just wasting your time. Whether bitcoin is used for legal or illegal transactio or whatsoever, it depends on individual choice.