OK, so using the alternative definition social democrat = socialist so your making a distinction earlier is redundant. No one argues he wants a violent overthrow of the government or Stalinist repression. But government is always coercive, so once he establishes a confiscatory level of taxation whoever refuses to pay will still go to prison, just like the guy in my quote (of course he'd need a like minded Congress and I don't see that happening soon, but that seems like a poor argument for electing someone President).
You already go to prison if you don't pay taxes in the US. See Wesley Snipes.