Romanticism per se isn't the problem so much as people who are drunk with it. Enjoying an overbearing aristocrat get his comeuppance is one thing, watching all of them being marched to the guillotine and cheering the death of the innocent is quite another. That is equally true of the bourgeoisie or the Jews or whatever the "oppressor" class of the moment happens to be.
I would add collectivism to the mix because only when one is subject to the dehumanization inherent in dealing with another person as a member of a class rather than an individual human being do we get the sort of outrageous violations of human decency we see in fascism, Nazism, communism, Jacobinism, radical Islam, and to only a slightly lesser degree in such class enthusiasms as feminism and racial movements from Mugabe's to Sharpton's.