I'm fine with showing these symbols in ways and forms that don't entail an endorsement. History books and other displays for factual purposes are obviously OK. Flying a flag out of your house is of course very different. Can you imagine a German flying a Nazi flag out of their house?
I would argue against all open displays of nationalism, of course. I for one don't celebrate a flag of a country founded by largely deluded religious fundamentalists who thought my ancestors were "vermin". I don't know why some people make exceptions just because "my country tis of thee."
Point being, we need to stop making exceptions for this sort of disgusting behavior.