Why don't we just institute a national call tax of 1/2 cent per call? It would be negligible for any legitimate call, but it would totally break the business m

Why don't we just institute a national call tax of 1/2 cent per call? It would be negligible for any legitimate call, but it would totally break the business model for robocalls which require millions of calls to get through. I assume an extremely small percentage of people actually buy stuff from robocalls. am i missing something?