OMG ok, so it says "the end justifies the means" which is something Jason Isaacs said as Colonel Tavington in The Patriot. Jason Isaacs also happens to play Lucius Malfoy, a Slytherin. Meant to be much?
It is just that Slytherin has a longer list of dark wizards. Gee, I wonder why. Maybe they are treated like trash by the other three houses and want revenge. Who would have thought that Slytherins have feelings as well?