The part I remember is Xander thinking about the Initiative (or some other similar group) and thinking about how Willow will be just as against them, because one of her relatives (grandpa maybe?) was in the concentration camps in WWII and told both of them about it. He thinks something along the lines of Willow being very liberal in just about every other aspect, but completely conservative when it comes to a government trying to control or experiment on certain groups.
I'm about 99 percent sure this is a Spander fic, I just can't remember what one, and that brief scene keeps popping into my head at random chanting 'find me doofus' and mocking my crap memory.
ETA: Oh yeah, I'm officially a great big, can't remember anything, doofus. The fic was Reconstruction by Wordsmith. Great fic.