"You cannot judge an idea on its merits without some preconception of what "merit" is or is not. This preconception may be completely idiosyncratic, or it may be in keeping with an established tradition of political thought. The point is that it must exist for assessment to be possible."
Point well taken, but evalutation of merit is not the same thing as political tendencies.
Personally I think you're muddling Politcal and Philosophical definitions of words.
For example, though a conservative may indeed feel that tradition is most important to society, it isn't simply because they believe that traditional in and of itself is intrinsically good. They reality is more subtle- tradition is good because something that exists for a long time is more likley to work better, is better suited to society etc etc.
Also, utilitarianism (or any other value system) isn't necessarily limited to one particular political interpretation or another. I could use utilitarianism to justify Facist domination of a majority, or I could use it to justify an extremely Liberal society where happiness of all persons is secured.
The distinction is when you decide HOW happiness, or equality, or freedom, is best achieved.
Personally, I have a hard time beliving that Liberals and Conservatives have such different justifications like you described, but then again I'm not American. :P
Oh, and in defense of the planned economy. It did work, despite horrible inefficiencies even then, fairly well during the war years.
If you want to maximize military production, a planned economy is much better than a free market in the short term. Hell, even Britain adopted an essentially planned economy during WW1.
As soon as your war ends though, or as soon as you start wanting to provide for people and encourage economic growth... well, thats where a planned economy fails horribly.
I'd say the main reason the Soviet economy failed was that it tended to ignore economics. :P