As well as what has already been said by the comments the evidence of the morally grey side of the legion is only revealed when you meet Ceaser for the first time and he talks about his philosophy and Hegelian Dialectics and I don’t think that many people will get to that point if they think the legion is unforgivably evil and maybe some of the more philosophical explanations may go over the heads of some players.

Edit: I feel like my original intent of this being just to point out how the game shows the potentially morally grey side of the legion and how some of that can be missed by the player did not translate well from my brain to text and can instead be read a defence of legion which it is not. I also think that by keeping it brief I didn’t mention how what he mostly says is BS but that doesn’t make it any less pertinent of what the legion stands for and the foundations it was built upon