An idealist is one who, on noticing that a rose smells better than a cabbage, concludes that it will also make better soup.
Did Mencken say that?
It is a nice line, but I would prefer to use it as a definition as a "theorist" rather than an "idealist."
Much of the trouble with the French is that they are fiercely committed to theory. It is an insight (which I took from Adam Gopnik) that explains so much. Only in the 90s, for example, did Communism get a really bad name in France. An important book was published documenting the millions of murders in the former USSR and created quite a stir among the surprised French.
Communism continued to attract twenty per cent of the votes there, because it sounded so good in theory.
The French would not be inclined to sample the rose soup. They would be satisfied with what theory told them about it!