That is weird. Totally in line with her worldview, but just so painfully simplistic. Even if Slytherin really *is* a house for kids who are just "innately bad" at the age of 11, it's even worse. Because after all, good kids - loyal, hardworking dunderheads or boring geeks, and most of all brave, popular good-looking kids - would never do something normal but mildly unpleasant like *eavesdrop* (and certainly not invent useful gadgets to improve on pressing their ears against the door). And of course, all those Machiavellian racist morons do *everything* that's unpleasant, much more than any good kid ever would.