For those that monitor the blogosphere, and specifically Economist.com's Democracy in America blog, you've no doubt followed the back and forth between Matt Steinglass and Will Wilkinson on any host of issues. Mr. Steinglass representing broadly the liberal view of things and Mr. Wilkinson the libertarian view of things. Without a doubt, it's some of the most intelligent debate between these two paradigms ("ideologies" seemed too rigid and not befitting the rationality they bring to the debate). I, perhaps narcissistic-ly, like to think the exchanges (typically in the comments section) between Ben, Colin (our foil at To Get Rich Is Glorious), and I are like a minor league version of the Steinglass/Wilkinson debates.
Course they still do it best, and when Mr. Wilkinson lays out some tenets of libertarianism including the belief that "Taxation is coercive but imprisoning the guy who nicked your lawn gnome isn't," you can expect that Mr. Steinglass would respond and so he did. There's a lot of good stuff in there, but specifically on the issue of "taxation being coercive" he notes that: "liberals think of taxation as paying one's fair share for the collective goods that make society feasible. Every society needs collective goods to function, including transportation and infrastructure, education, the justice system itself, and so on... Payment for those goods cannot be left voluntary, as ultimately everyone would welch."
This completely captures why I think taxation is legitimate. Of course, one could say, and Colin as suggested, that you must have pessimistic view of people if you believe they won't voluntarily contribute what is needed for the general welfare. I think that makes me a realist and a liberal.