Well, that may be the case on the continent, but in England you can definitely call someone a left-wing liberal. Especially if the person speaking is as right-wing as a Malfoy. Liberals aren't 'conservative light', they're much more of a political mish-mash, generally. And liberals with a small l are found at all ends of the political spectrum. With respect to something like House-elf rights I'd say that Hermione's position is exactly left-wing liberal.