The word derives from "de" and "bunk" -- an older word effectively meaning "bullshit". In other words, to "debunk" a claim means "to remove all the bullshit" from the claim.

If a claim or argument is indeed, for all intents, a "bullshit argument", then it is quite fair to "debunk" it. But this isn't how most people use the word.

Most people seem to say "debunk" as a means of saying "refuted", or worse, "rebutted".

Just because an argument can be refuted doesn't mean it was a bullshit argument. Quite often an argument is perfectly valid, and only fails when the premises fail to be 'proven' conclusively. Not to mention that more often than not, 'proven conclusively' is a highly subjective notion to begin with.

To say an argument was "debunked" is effectively a very rude way of dismissing / diminishing the person making the argument as being full of bullshit, when in fact their argument may have been a perfectly valid one, and possibly quite sound even, and may even have been useful in furthering the conversation.