If the incommensurability argument (which applies to science and makes it impossible for Lavoisier to talk to Phlogiston Theorists, for example) I'm not sure if it can be expanded into the political or moral realm.
Science deals with facts, politics and morality deal with something profoundly different, ie values.
If rational comparison cannot be used, and our worldview is based not on reason but on emotion, preference, desire &c, then moral disagreement can only be resolved through rhetoric, persuasion and, ultimately, force.
Wait a minute: that is exactly what happens! You might indeed be on to something, even if it looks like a fairly unpleasant something.
It might be pertinent to point out that Liberalism = Laissez-faire capitalism, so I'm not sure what you are getting at there. (Possibly you are confused by Coulterian rhetoric, which uses an imaginary definition of the word Liberal, for no good reason that I can see, but a trip to the dictionary can easily put you straight on that). And Liberalism doesn't exist any more anyway, because of it's failure to deal with massive crises (like the 1930s) or to provide people with a decent quality of life (like in the 1800s) and it's inability to manage the economy (even Reagan didn't stick to his Liberal guns when the chips were down).
Well I explained that badly.