But what is there in this song to make anyone feel it would merit censorship? (Unless it was sung in a way that seemed to celebrate the events contained, but that's not the song, it's the performance.)

Songs can exist in many variants. I see nothing wrong with choosing a variant that fits in with what you wish to say. Or, for that matter, giving birth to a fresh variant of your own. The variants have to have come from somewhere, after all, and the history of a song's development hasn't necessarily stopped, just because it's reached you.

There's an analogy with jokes. The same joke can be told in a way that is racist or non-racist. And there's no duty to tell the racist version just because that's the way we heard it, or to refrain from telling it in some other way.

For example, the joke about the men talking about how they named their children after various saints, because they were born on the saints' days, and then one says he called his son "Pancake" for the same reason - it actually becomes unfunny, when it's told in an Englishman, Scotsman and Thick Paddy way, whereas if they are just three unspecified friends, it can be quite a good one.