Oh, fandom. Again? The first time I ever heard the word "miscegenation," I was fourteen years old. It was in class discussing Deeply Stupid Things in Alabama's Constitution. I have never heard it meaning only "the mixing of races"; it has *always* meant, in my mind, a piece of Alabama's past which was shameful and awful and horrific.
And I just kinda... okay, so maybe you didn't *know* the context of this word, daily_deviant mods. I can believe that! I really can! A lot of people aren't comfortable discussing racism and so forth, maybe you'd genuinely just *never heard that word*. But, um, dude, the proper response to having someone email you and tell you "your diction is offensive and here's why" is *not* to say "oh well! tee hee! big deal!" The proper response is to apologize and change your word choice to something less loaded.
(If you don't know what I'm talking about, check
here,
here,
here, and
here.
Also, still not dead.)