Guilt / Innocence is determined only after due process has occurred, i.e. their day in court. If say, you were to argue that AFTER being found guilty in a court of law their car should be towed / impounded then I would have no cause to argue with you (although I would still disagree for numerous reasons)
If law makers intended to to have Towing / impounding of ones vehicle part of the punishment of driving without a license they would have written it into the statute governing the offense. As it stands right now, the removal by the state of vehicles in the roadway can only be reasonably described as a public service of removing hazards and/or blockages to the public roadway. This being said the state's ONLY interest is that the hazard / blockage gets removed. Why does it matter who removes it? While it may feel punitive at times when your car gets towed it is not the intention. Point of fact: Cars get removed (towed) when parked in front of a fire hydrant not as a function of punishing undesirable behavior but as a function of ensuring that the fire hydrant be available should it be needed.
AND.... Lets just say it WAS intended to be part of the punishment.... why would you apply the punishment BEFORE someone has a chance to argue their guilt or Innocence. It makes no sense