Any currency can be used for illegal activities. Why the dollar is the most popular currency for these purposes?
because dollar is the most common currency in the world.
In general, bitcoin has more prospects for use in this area, because of anonymity
Exactly, that is why we should not get surprised if in the future becomes the number one currency of the world then bitcoin is going to be used not only by good people but by bad people as well and to be honest there is nothing we are going to be able to do about it.
I do agree but i don't think that the government will approve that bitcoin should be the number one currency. They will just agree to the idea of bitcoin can be alternative currency in terms of global transaction. If bitcoin replaces fiat then the governmen cannog manipulate the money cycling over their economy. In other words, they will loose power over their nation.