Ya! Trusting Snape to do something like that is like trusting an angry Cobra not to bite you! The stupid fool believes in the Pureblood superiority. The Pureblood superiority simply put is breeding yourselves into extinction! Following said ideal means sooner rather then later marrying your first cousin as that's all that'll be left. Killing off the muggle-born, half-bloods and full-bloods means cutting drastically cutting down of your potential gene pool before it can do you any good. The Gaunt family is the perfect example of what the Purebloods expose. So simply give them what they want and withdraw the others from Briton and close it off from the rest of the moronic European Purebloods. Leave them isolated and let the rest of Europe watch as those in Briton rapidly decline and die out. Unfortunately, Fumblewhore and the Ministry won't allow that to happen. Fumbles because he has a prophecy he wants fulfilled. Of course, he doesn't want to get his own hands dirty so he has shifted the responsibility to a child.