(It's very aggravating that the plane of Acheron is Lawful-aligned, because it seems like exactly where this sort of endless, idiotic battle should take place. While the 'I'm right and you're wrong, so shut up' mentality is pretty much Lawful and thus Acheron's status as a Law plane is quite thoroughly valid, it still seems as though a Neutral version of the plane of never-ending battle would be just the place for a bunch of Skarn and Rilkan Incarnates or something to duke it out for all of eternity.)
Now this part, on the other hand, I would say is debatable. Ignoring for the moment the +8 level adjustment on the vampire template, if we assume that vampires continue leveling at about the same speed as humans throughout their substantially longer lifespans, and that they can go into epic levels or even triple digits given enough time, which they are...what they become capable of accomplishing gets into the realm of literally godlike power, and I can see a very sensible argument that says a civic-minded vampire with 47 Wizard levels can accomplish more good than all the people he eats, combined, could hope to achieve in their entire lives. He could very justifiably claim, on the basis of his public works, to be the foundation of his entire society, and as much worthy of protection as any of our world's holy books or institutions of law or bodies of science or anything like that. For him to get inevitably slapped with the evil-stick, even in the event that he is an immortal Gahndi-Lincoln-ChuckNorris-etc., who makes life better for millions of people for 8 hours every day and then eats a dozen or so of them for the next 8 hours before going to bed...well, hopefully my point can be vaguely glimpsed in this cloud of words I've exhaled here. (Sorry, it's late enough in the by-my-standards-evening that my command of sentence structure is beginning to gain the Incorporeal subtype.)Objectively if we measure good and evil as the weal or woe of an action then slavery results in greater harm that good for the majority, as does the killing of humans to keep the vampire alive. They are objectively evil acts.