Insecure pseudo-intellectual jerks -- the types that thrive on IRC -- love these sorts of arguments. It's an easy way to win a fight and assert your superiority. It doesn't take much for the people who make a fuss to know the supposed original usages. And the terminology is commonly used interchangeably, so the opportunity to 'catch someone out' frequently arises. The meaning of a word like this usually derives from how it is used. If 99.9% of people think of hacker as a general term (that would include crackers), then that is the effective definition of that word. It's also important to be able to distinguish between being homosexual and being happy. That doesn't mean the correct route is to chastise people who use gay to mean homosexual.
The hacker/cracker debate is, I think, similar to the "begs the question" debate (whether you can use "begs the question" to mean "asks the question", just because everybody does). And in both cases, I think that the distinction is more important than the distinction between, for example, "gay" and "happy". The difference is, I think, that the terms have very different implications. It's not as simple as the word being redefined in popular culture when the meaning and intent of the original word is lost.
Maybe people enjoy arguing about the definition, I wouldn't know (I don't hang around people like that), but that doesn't make it any less important to avoid adding any more ambiguity to an already insanely ambiguous language.