Whenever I see someone say that Edelgard is the villain because she started a war, and "the end doesn't justify the means" I'm always reminded of an example I heard during a philosophy lesson in high school
"Imagine you are tied up to a chair, and you can only move one arm. You have a gun with you which has a single bullet in it. Alongside you there are some defenceless children sleeping, and a grown-up man with a knife, who states that he will kill all of those children, and procedes towards them.
What's the right thing to do? Killing the man in order to save those innocent children or not doing anything and let those life be ended by a bigger force?"
That example is litterally were Edelgard is now: She is the tied up man, the Church and the Nobility system are the killer and the defenceless children are the people of Fodland, who all suffered from how the society is structured (just take a look at Sylvain and his brother, Lysithea, Edelgard, Mercedes just to name a few who all got their lifes screwed up because of Crests), a society so broken that it will never recover by itself.
That bullet, the war, is Edelgard's only chance because, thanks to Lysithea, we know that people who had a second Crest transplanted on them will live a far shorter life, so she doesn't have the time to come to a peaceful agreement.
Also a little side note: Edelgard never justifies her actions, she knows that this war will be a massacre, but she feels that not doing it will be worse. War destroys lifes in the immediate future, but after a couple generations people and states do recover (take a look at Europe after WW2), while a society like Fodland's will keep destroying lifes behind the shadows, and might as well do as many if not more victims than a single five year war in the span of a couple of generations.
Still, people describe Edelgard as someone who will do anything fir her cause, but she also doesn't do anything that isn't stricly required for her cause. She can spare Claude and all GD members in her route, she doesn't kidnap or murder innocent people and she surely didn't order to burn a whole city full of civilians just for having tactical advantage.
Also Dimitri is no different, just like Edelgard he is a psycopath in all routes except his own, someone who doesn't even consider doing a truce with the Empire not because of different ideology, but because of a mad thirst for personal revenge, and a misplaced one at that. Imagine if during WW2 the Allies didn't united themself because they hated Roosevelts' face and how that would have turned out. Dimitri in the end is a good person scarred from war, and that makes him a terrible leader to follow, since a leader needs to guide his troupes with rationality and control, not follow their own twisted personal desire of revenge.
Just take a look at any Hystory book and you will see how some ideological war were essential for arriving were we are today. The French Revolution, the Soviet Revolution, the Independence War and so on. Those who are in charge and use their power just for themselfs or how it better benefits them will never let it go without fighting, that's why revolutions happen sometimes. Was starting a war against Hitler an inexcusable bad thing to do, or rather a terrible sacrifice in order to avoid a far worse outcome?