"What is there to negotiate, given Republicans are demanding unilateral concessions in exchange for doing what they themselves say is necessary for the good of the country, i.e., keeping the government open?"
This is a very precarious position the GOP has put itself in. Ignore for the moment the fact that they're flagrantly disregarding the results of the last election, in which they lost all three major popular vote counts by large margins. The fact remains that not only do most Americans vehemently oppose shutting down the government to delay or disrupt implementation of Obamacare, but they do so in spite of the fact that they have mixed-to-negative opinions about the law. Yes, I realize that I've repeatedly said that polling about complex laws is fairly meaningless, but the important takeaway here is that the GOP's current strategy is viewed by the public as exceedingly extreme.
But let's leave the murkiness of polling behind for the moment and think about the GOP strategy outside the context of public opinion. Their strategy is to shut down the government (and possibly cause the U.S. to default on our debt) out of a desire to disrupt Obamacare. But here's the kicker: Obamacare launched today in spite of the shutdown. It was largely unaffected. That seems like something of an oversight on their part.
So let's review: the GOP is shutting down the government (and far more importantly, threatening to breach the debt ceiling) to try to delay Obamacare, and yet Obamacare is unaffected by the shutdown and launches on schedule. Oh, and public opinion (and election results!) does not look kindly upon their strategy in the least, giving them little time to wait for the Democrats to cave.
Like I said, precarious.