Black Mail

I was arguing with one of my more liberal professor's a bit after a class concerning Ayn Rand. I was trying to make the argument that force fraud and theft are the only true types of coercion that the government should be concerned with preventing. He, on the other hand was arguing that other types of coercion are just as bad (or at least that socialists have a strong case in saying so), such as the kind of "coercion" that occurs when someone is given the choice between some bad natural result, such as starvation, and employment under harsh conditions. I was on pretty solid ground for most of the conversation, but he stumped me rather well when he brought up the subject of black mail as a form of coercion. The practice is widely regarded as being equivalent to theft or assault, or any of the commonly held acts of aggression that libertarians et al. are typically set against, but it really has nothing to do with the use of force, fraud, or theft. It doesn't use any physical force against anyone, it doesn't use fraud (In fact, the whole point is that it typically threatens to declare the truth), and it doesn't steal anything from anyone. All it does is give people an opportunity, just like an employment opportunity does, that people can take up if they wish to avoid some negative situation such as not having enough to eat, or not being found out.

I have to admit, it was a pretty good argument (To be expected from the high-quality faculty we have here at UVA I suppose), and I am left to conclude that libertarians really can't consistently claim that black mail is coercive in the way that we declare should never be allowed. And if we don't declare black mail to be one of the few things that it would be OK for the government to ban, then are we doomed to be made to look ridiculous? Or does anyone have an explanation of just exactly why black mail is more coercive than employment opportunities?