The political calculus is something like this:I can't speak to what was going through his head when he wrote it, but I'd like to think that he was working to expose some of traditional libertarianism's fundamental weaknesses. I would consider myself to be more of a 'democratic liberarian' than a 'real' libertarian - that's a small 'd,' though I'd also hope the Democratic party picks it up. The state does actually have a legitimate role in promoting free and fair elections, thus ensuring political freedom - the most important kind.
"Those kooky libertarians are too radical but they do strike a chord with all that 'liberty' and 'individual rights' and 'get the state of my backs' stuff that spout... so we will give people the impression that we also care about that stuff too by calling ourselves 'libertarians' as well but then add 'democrat' (or 'socialist') to let people know that you can have that good stuff as well as nationalised healthcare, a regulated economy and a big government."
If you doubt that then just read some of the comment on that Kos article.
Kos is NOT engaging in an intellectual debate and it is preposterous to think otherwise. He is engaged in developing a political tactic...
The basic problem with 'real' libertarianim is that it doesn't have any ideas about how to actually come into power. This means either that it won't come into power, dooming it into irrelevance, or else it will have to come into power through force, in direct violation of its own tenets. Democratic libertarianism answers that question - libertarianism tends to sell well in polls, so more democracy will help it acheive more prominence.
In addition to cleaning up libertarianism, my belief is that this will help focus the Democratic party on a core issue - cleaning up government. This will also give a direction to move towards in the future, which right now is its most pressing need.