My view is perhaps a little biased but im Canadian, and seeing a group out for genocide of people they consider inferior and at the same time talk all about that god bless the united states stuff when they really dont have the common man in mind.
The Enclave definately have a lot in common with the Nazis, who "only" wanted to rebuild and strenghen Germany ... and relocate the people deemed un-German, such as Jews, homo sixuals, Socialists, etc. Later, during WWII, it became to expensive to forcibly relocate these human beings, so the Nazis decided to murder them.
Why does everyone assume rebuilding America is a good thing?
I suppose it depends on which America one would want to rebuild? The one that caused a nuclear war? The semi-fascist utopia of the Enclave? Or an ordered government learning the lessons of the previous 4 centuries? The last one does not sound so bad. The middle one may be preferable to the people in the Wasteland.
Nazis: The World was fine when they tried to change it.
I suppose you never heard of the http://en.wikipedia.org/wiki/Great_Depression? Due to having to pay war reparations, the Germans were particularly bad hit, with an unemployment rate of 30% in 1932 and an insane inflation. The Germans at the time definately did not consider the world to be "fine" - if they did, 1/3 of them would not have voted for Hitler.
The Enclave: Destroy mutants so humans can reclaim the globe
Mutants: Any and all who does not have human DNA, but once had.
Humans: Well, humans. Homo sapiens.
Unless I missed something, they also considered slightly irradiated humans to be mutants, who had to be exterminated to revive the "pure" human strain. Disturbingly similar to Nazi claims that "non-aryans" should be deported (and later exterminated) as not to "pollute" the "aryan" race. Incidently, both ignore science fact. The Nazi dream of an http://en.wikipedia.org/wiki/Aryan race that never existed. Similarly, "pure-strain" humans is a contradiction of terms. All humans have small mutations from background radiation. It is how the species evolve.
To get back to the original question on the evil of the Enclave, my opinion is that I do not believe in the concepts of Good and Evil. They are only in the eye of the beholder. Would I fight them? Yes, mass murder is not an option for me.