Because of our own mythical political history, Americans are especially disposed to thinking of governments as ideologically motivated. There’s some truth to that: it’s easy to pick regimes in history that had a central organizing ideology. Most of these I would place in the 20th century, but not all. The Nazi regime comes to mind: although in the middle and lower levels one could easily pick out mere political opportunists, the leadership was made up of true believers. The Soviet Union is similar, although subjectively it seems like it had a smaller percentage of true believers domestically (and a higher percentage of true believers abroad).
Citizens of the United States are taught in their impressionable years how the foundation of the US was a total break from history. This idea comes from the Yankee Puritans, although the Puritans intending to found a new society that would be a light on a hill for the rest of the world to imitate would have balked at other American regions with different customs, laws, and especially religious practices being part of it, or its being a secular light in any way.
What are the effects of seeing governments this way? One ought to be a tendency to guard liberties jealously from overreach, maintaining the supposed moral purity of the system. Each new government power would be not just a small practical increase, but a symbolic leap into citizens’ private sphere and away from a sacred purpose. Early on this seems to have been what happened.* Yet as the power of the government grew slowly over time**, resistance itself become largely symbolic. (Witness the recent fury over Catholic employers having to cover birth control through their health plans. Without denying the importance of the issue to many people, what is being argued here is just crumbs compared to what could be debated.)
Once that blurry line was crossed long enough and defense of the continuity of the system was a defense of government power, we’d expect that this would make Americans more ready for war. Still maintaining that our government was in principle correct as a matter of course, foreign governments must be wrong when in opposition to ours. In any sustained conflict, foreign governments must be wrong in principle.
As I began by pointing out, there were ideologically motivated governments, and most of them were what we could objectively describe as “bad”. But the conduct of our own government hardly makes it seem ideologically motivated in a way radically different from other governments historically and currently. Nazi scientists with potentially no political motivations were used by the victorious Allies after World War II, but spies with overt political motivations were also used. One day they were enemies, and the next day they were valuable assets to be protected. It was argued that this was in the service of a greater good, but that greater good was pretty nebulous and ambiguously served. The conduct of other governments, Nazi and Soviet and otherwise, also makes this point clear. Various currents in Imperial German and Russian foreign policy continued to be major components of Nazi and Soviet foreign policy, even if the vocabulary of their articulation changed.
The point of a lot of libertarian scholarship has been to point out that the US government is not fundamentally different from other governments. It does not matter if that was the stated purpose of the scholars; viewed from above, this is the theme. True, we have a written constitution that sets us apart, but this constitution hardly has any real power in setting limits to government action. The usual rules and analytical tools are far more useful for understanding the US government than any appeal to myth. The proximate purpose of new and continuing scholarship is to convince the not-yet-convinced of this truth. The ultimate purpose is to know and generally agree on what we’re dealing with to help us deal with it better.
* I’m sure I hardly need to point out that the liberty to own slaves is not a real liberty, conflicting with and negating the valid ones. But that contradiction does not bear on this discussion.
** This is what government powers tend to do. There are exceptions, though it is an empirical question whether the most common exception is restriction of government power or large increase of government power.