[pdonis]

>One of the defining properties of liberals and, even more, progressives is idealism.

If you mean idealism as a way of conducting your personal life, I don't think it has anything to do with any particular political persuasion.

If you mean idealism as a political philosophy, while I agree this is a defining property of progressives, for liberals, at least the classical liberals that were the original referent of the term, no. (Today "liberal" pretty much means the same thing politically as "progressive", but that wasn't always the case.) Classical Enlightenment liberalism was highly suspicious of idealism as a guiding principle of politics and public policy, because it recognized the limitations of humans. We are simply not smart enough to come up with useful idealism on the scale of a country. Every time we try, it causes far more problems than it solves. Classical liberals preferred to let institutions on a larger scale evolve from the bottom up, as people exercised their individual freedom of choice on a smaller scale and were held accountable by the people they interacted with.