Foseti comments on both exit and left-libertarianism, and I'm inclined to believe he misunderstands both, and that the misunderstandings are related.
There is an entirely different KIND of relationship between me and the guy who sells me oranges at the local farmer's market than there is between me and a robber.
In case #1, I can (a) decide to buy oranges from a different guy, or (b) decide not to buy oranges. My interaction with him is entirely based on positive sum trades. We are BOTH better off, by choice, and in our own cognition after we trade than before.
In case #2, (a) do as I'm told, (b) get shot, (c) both. After the trade, he is better off, and I'm screwed.
The difference is simple...and obvious to anyone who isn't trying to argue something that relies on conflating the two. In one case, it's trade/ voluntary /autonomy/etc. In the other case...it's violent evil thuggery. Why do we organize to suppress #2. Because we all know it's bad/not fair/immoral/strong taking advantage of the weak. Duh!
Case #3 is the case of government monopoly: (a) do as I'm told (b) get shot (c) go somewhere else where I have the same choices. Fundamentally, it's an interaction where I get screwed by having the interaction at all.
Exit: The notion that voluntary interactions are better than involuntary ones. Not real complicated.
Libertarianism is the notion that #3 is roughly equivalent to #2.
Left Libertarianism is the notion that many things that we think of as case #1 are, due to the actions of thugs who label themselves a government, much closer to #2/3 than #1. Libertarians who lean mildly left think that IP is 90% government violence deployed to make rich folks richer. More left would be the position that the Federal Highway System constitutes a massive subsidy to large corporations contra smaller local enterprises. Further left-ness would specify that any property rights not based on value-added use are a case of #2/3 instead of #1.