I'm not comfortable with the "evil for evil's sake" bit.
About time somebody got back to basics.
Khan wanted power, yes, but I think he believed his motives were benevolent, that he deserved to rule for the greater good.
Who cares what Khan believed? Evil is evil, whether or not Khan THINKS he is evil does not change the fact THAT he is.
And anyone who thinks Khan is such a good guy should really read Seeds of Dissent