By that token, there's no such thing as a just nation--never has been, never will be. Even a nation that declares itself neutral in a conflict can be condemned by some as evil for turning a blind eye to injustices.
Very true. Interpretation of such things are a matter of opinion and personal philosophy, as I've pointed out earlier. For instance, there remarks on such things as slavery once being a popular circumstance. Where, I compared such matters to events occurring today, such as where people are being locked in cages for smoking plants. Absolutely barbaric. If you ask me, so too is killing in any form unless it's necessary to prevent the harm or oppression of others. If someone points a pistol at me today and announces their intention to kill me, I absolutely welcome any policeman to shoot that person. However, if you're going to kill other people, If you're going to kill another human being, I think you better have a real good reason for doing so, and that you should be absolutely certain about the authenticity of the information and the accuracy of the analysis of that information which you've used to justify killing. As such, remaining neutral isn't necessary unethical. If you're not certain which option is the ethical choice, or if you're not strong enough to overcome your unethical foe, it may be wise to not commit yourself.
But yes, a neutral nation could be argued to be "evil" for its neutrality. Anything could be argued to be "evil" for any reason, but at the end of the day what's "good" and "evil" isn't universally agreed upon. Ethics is a matter of opinion. It's also a matter of perspective, including whether or not the individual has placed any thought into the subject in order to have a well developed perspective. Consider conscription for instance. Many nations, including the United States until very recently, would compel its citizens to serve in its military. Many nations still practice this, and the United States reserves the right to resume the Draft if the government deems it necessary. However, conscription is the act of forcing people to perform labor, which is slavery. I can't be sure, but I don't think conscripts/draftees typically regarded themselves to be slaves. They just never considered it, or maybe they would disagree, arguing that they're were/are still free, despite that they lack the freedom to stop performing the labor demanded of them. The world is filled with these things. Things that people don't put much thought in, and other things where people can't agree on the interpretation.
Is spanking a child ethical? That is, a large adult physically striking a small, helpless child, or as it could otherwise be perceived, a parent disciplining their child in order to correct their behavior to the end of education and forming a more decent future adult. A matter of opinion. Is contraception evil? Also a matter of opinion. Is the Federation ethical in this instances I've cited in this thread? I don't believe it is, but as you can see from the responses in this thread, not everyone agrees with that judgement. It's fitting, I think, considering the TNG series so often concerned itself with ethical dilemma and debate.