Oh. I apologize and admit to my mistake: unlike the better sort of Slytherin their mentality isn't exactly Machiavellian, though it is take-no-prisoners in its own, different way. I'd still like to hear a more detailed study of the difference between the two, for the sake of moral clarity (heh) since in my dislike for them I have unwisely lumped them together, which is a mistake, which needs to be corrected.

As a desperate save for the sake of fanfictionish silliness, I'd add that the same way conservatism has turned out very different in the USA and the UK, it's fairly plausible that the USA offshots of the House Of Slytherin may have developed differently from their continental peers. You wouldn't know of any fanfic that properly explored Potterverse Magical America, would you?

...Now I'm really far off-topic.