Vassalage is being a subordinate or dependent of a person. This does not exist in the modern state. You cannot be a vassal to an abstract state structure, only to an individual.
Per definition of the word, perhaps. We have more freedom than the peasants of the middle ages (but less than the lords, unless we're fabulously wealthy) but we are still subject to the laws of the "abstract state structure." Like the peasants whose ancestors helped create feudalism (or vassalage, whichever you prefer), we are born with duties, even though we never swore fealty to anyone. If you're only arguing that the word vassalage cannot be used to describe this, then that's alright with me. That wasn't my point.
Modern scholars of the Middle Ages no longer use the term "feudalism" to refer to medieval social structures. Instead, the use the term "vassalage." A system in which individuals are subordinate to one another is one in which social inequality is a condition necessary for the structure itself to exist. A system in which all individuals are equally subordinate to the state is one in which social equality is assumed to be the natural condition.
Well, whichever term "modern scholars" prefer. In Sweden, we still call it feudalism, so you'll have to forgive me there. Strictly speaking, vassalage is only inequal in-so-far that logically not everyone can afford to be a knight, unless they live in say, a fantasy kingdom where everyone can afford to own a horse, an armor and weapons and still manage to somehow feed themselves while they train rigorously each day. Not so likely, but who knows where Sir Cedric lives?

Again, if you just want to argue that vassalage tends to disenfranchise most people from lordship, that's fine by me. However, "a system in which all individuals are equally subordinate to the state" is an utopia, no matter how much our well-meaning elected officials extoll the virtues of his or her particular system.
Therefore, to suggest that the modern state is a form of vassalage is incorrect. When George Bush becomes president, people do not become subordinate to him personally; they pledge allegiance to the flag not to George W Bush. The reason we pledge allegiance to states and their symbols rather than to individuals is because modern social contracts are specifically designed to prevent vassalage. The founding fathers of the United States created a state structure that would prevent legal subordination of individuals to other individuals. Ben Franklin and company would roll over in their graves if they heard you arguing that equality under the law and vassalage were indistinguishable.
Indistinguishable? Very few things are indistinguishable. My argument is that vassalage and, shall we say, citizenship, are in the same vein, not that they are the same thing. If you want me to stop using the word vassalage to compare them, that's fine by me. However, just because sandstone and granite are both rock doesn't make them indistinguishable from each other.
This is not an argument about the freedom of americans, nor an argument that tries to imply that any other system on earth is more fair.
The casual comment I originally posted as a reply to your statements about vassalage (you yourself used the term feudalism, by the way... so I don't quite understand what your point about modern scholars is?) was not very well ordered--I'll give you that as well. Still, I thought that people would give me the benefit of the doubt and manage to decipher it. Clearly my paragraph was convoluted beyond disintegration, however. Sorry about that.
Prostitution is not inherently non-consensual. Feudalism is. Prostitution is not inherently unequal. Feudalism is. Prostitution is not inherently disenfranchising. Feudalism is.
Let me say this: Feudalism is a sub-system which required a monarchy (generally) to be in place. The people in a monarchy are already disenfranchised and unequal. If you want to argue that feudalism/vassalage
further disenfranchises the people by separating them into nobles and commoners, that's fine by me, but it sounds a bit like saying "he died of blood loss" of a person who was crushed by a 1,000 ton boulder.
Also, feudalism was no less consensual than being forced to prostitute yourself to survive--during the first generation.

Obviously, everyone born from peasant children already had that choice made up for them. That point might not have been within your purview, though.
EDIT: If I lost sight of your original point, pardon me. I've focused merely on countering what you said in the argument spawned between the two of us. For instance, it might be pointless to say that monarchy is the culprit rather than feudalism.
EDIT (again!): Don't misunderstand me; I'm absolutely not saying that feudalism/monarchy was or is as fair as democracy. I'm proud to live in a society that adheres to the principles of "Ben Franklin and company."