It has nothing to do with being a goody two-shoes. In a lot of circumstances, the "evil" is better, simply because of misperceptions on the parts of those who do the labelling. This, however, is NOT one of those cases.
The Sith Order is predicated on doing whatever is necessary to achieve one's own ends. There is no honor, only what is good for self. There is only destruction. There is no good in this. To say otherwise is just stupid. To justify it as "social darwinism" is not only a misinterpretation of what social darwinism actually is, but also ignoring of the fact that such justifications have rarely held any commercial or political weight in the past.
Look, I'll be the first to admit that the Jedi Order is flawed. I don't even particularly like it. I'm not a blind follower, and agree that the Order's stubborn insistence on following a Stoic philosophy is ultimately what doomed it. Qui-Gon alone understood this, and rejected stoicism in favor of romanticism. His Republic was a fusion of the ideals of Plato and Whitman, and had that been the prevalent line of thought of the Jedi Order, the Council would have found itself invulnerable to the Sith.
The Sith, on the other hand, are basically the Church of Satan, with a bit of an anarchistic bent thrown in to spice things up and provide some more dramatic contrast. Don't be deceived by the name, though- the church of satan is basically just a bunch of naturalists- advocates of the same line of darwinist thought that you've spouting on this thread. I understand fully where you're coming from, but that doesn't change the fact that you are wrong.
So don't try to tell me that I don't understand the issue. I most definitely do, and can see where you might be coming from, to the point that I'd agree with you in those situations where it has even a remote degree of applicability to the issue at hand (the issue being that "good" and "evil" are not always as easily discernable as those who proudly wear the labels would have you believe).
The major strength of the Sith way is, indeed, its seductiveness. It looks as though you have succumbed to it... are you ready to accept the consequences? After all, you cannot say that such a way is better without being willing to withstand the negative consequences of it. In the case of the sith, the negative consequences are anarchy. Would you prefer anarchy? Is that right? Of course it isn't.
The Jedi may be flawed, but their intentions were in the right place. Throw in some revelations in Episode III, and you have the makings of a very salvageable order. The Jedi are interested in preserving the integrity of the government- of bringing and keeping the peace. Can you honestly say that warmongering by the select, powerful few is better than this? If you can, then you're either dim-witted, or supremely confident in your survival skills.