As always, it depends what the song is! You can't simply say "you should/shouldn't sing song X because it's "about" this or that".

I recently learned "The Kaiser" by Pink Anderson. It is sung from the (ironic) point of view of Kaiser Wilhelm II. It contains the immortal line "We conquered little Belgium/and France will soon be ours". It has a fair bit of jingoistic flag-waving about Uncle Sam's boys. It is distinctly un-PC.

Why do I like it? Ultimately, I reckon, cos it's ridiculous: it boils down global warfare and killing on a massive scale into a puerile scrap between "our boys" and "their boys" in a playground. There's a kernel of truth there. Pink Anderson sings it with just the right amount of deadpan and humour.

Of course, you certainly couldn't sing it if it were about, say, the Bosnian conflict, if it concerned Ratko Mladic for instance. (Unless you were trying to make some kind of confrontational art statement, I suppose.) That's the thing about history. Ultimately, the passage of time turns today's mass murderers and serial killers into boogiemen and folklore.