Leaving aside the specific laws in question (to avoid derailing this into a discussion on the sanity of drug laws), it seems completely reasonable to seize assets generated by illegal activity, if such activity has been proven in a court of law. The accused remains innocent until proven guilty, and the seizure should be tied directly to a guilty verdict and included as part of sentencing. (In the case of a crime involving one or more victims, most notably theft, the proceeds should go directly to those victims.)

Today however, the processes for property seizure occur almost independently from the procedures of the criminal justice system; seizures can occur without any guilty verdict, and there's no guarantee that property will be returned to innocent people.