I completely agree that once they say, "get out or we'll take you out," you should get out peacefully, and pursue any remedy afterwards.
However, I also contend that in a case like this, where the passenger was not any sort of threat, it never should have gotten to that point in the first place. The idea of preserving civility by preferring nonviolent responses says that the passenger should have left peacefully, and that United never should have tried to force him off.
This is what I mean by "applying them only to one side." Both parties were in the wrong, but you're giving the one with all the power (and the one that started it) a free pass, and focusing all of your criticism on the customer.