What's going on here is pretty simple to explain: Philosophically, the Slashdot community is probably pretty libertarian minded, but politically they tend to lean to the left, and here's why:
The Republicans are a pretty big party, composed of a couple of different aspects. Essentially you've got your foreign policy hawks, your social conservatives, and your economic conservatives. For the past 20 years, the Republican party has been controlled mostly by the foreign policy hawks and the social conservatives, and the economic conservatives have remained only a steady undertone to the whole party's platform, but they've actually consistently remained there the whole time. They're the few who fight for limited government (even against the rest of their party oftentimes), clean and transparent government, against earmarks and pork (definitely against their own party oftentimes), and many of the other policies that Slashdotters (and Americans) in general seem to want.
Slashdotters in general have fallen for the same BS that America as a whole fell for: the socially conservative/foreign policy hawk members of the Republican party proved to be somewhat corruptible - especially as that was an aspect of government that those Republicans didn't really care much about - so most members of the Slashdot community have done what seems to be the obvious choice, and embrace the main political opposition to the Republicans, the Democrats. Even though the Democrats stand for almost nothing the slashdot community values in government. Honestly, have you looked at the record of any Democratic politician? Take a look at how many nominations Obama's gone through that have corruption issues. Or how the Democrats have been running the stimulus bill through without letting anyone (even other Dems) get a good look at it. Or just look at the leaders of the party: Reid and Pelosi both have plenty of financial scandals, and yet America (and the slashdot community) somehow just looked past their actual records and took the "Culture of Corruption" bait in 2006 when the Democrats said they would operate a cleaner, more open government.
What compounds the confusion is when America and Slashdot remember the few triumphs the economic conservatives have actually had in recent years. They get attributed to Clinton! When Newt Gingrich led the Republicans back into power in Congress in 1996, enough economic conservatives came to power that they were able to do two key things that the Americans loved: Pass a balanced budget, and reform welfare. The balanced budget led to a surplus (rather than a deficit) and welfare reform has been amazingly successful. And somehow they constantly get attributed to Clinton, even though he vetoed both multiple times until they were passed with veto proof majorities (and then he signed them so he could have his name attached in the off chance they worked).