the whole idea of anonymity at the internet is better for everyone, especially for criminals. making an instrument which can be used for both good and bad purposes sounds a bit concerning. moreover its not possible to control it.
I do not think that anonymity is necessary for criminals. People for many reasons want to remain anonymous. And not necessarily that they are doing something bad or illegal.
I agree, there are many reasons to remain anonymous for a good reasons. but criminal still exist and it still attracts lawbreakers because of such an anonymity.