I really don't even think that the most brutal of the Yeerks could be considered evil or wrong.
Think about how they are, and how their society works. It's true that there are some Yeerks that have a more utopian view of what they want their world to be like. But they aren't in the governing body for a reason. They can't openly say that for a reason. It isn't how their culture was structured. In order to transform their society into a society that only takes willing hosts, millions of Yeerks would go without hosts. Millions would be sentenced to a life that would essentially be considered hell compared to what it was. How do you choose who gets to see, hear, and smell and who gets to live in the dark? Even if we assumed the entire Yeerk race was nothlitized into humans or whatever creature they chose, to do so would cause massive chaos and unrest in their society. They would have to separate the ones that would abuse that power and the ones that could live peacefully, how do you do that without legislation that would be brutal in its own rite? If anything, THOSE ones would be classified as 'wrong' because they were hurting the rest of their race. They were adapting to ANOTHER culture's way of life, not their own. They were sabotaging the people they came from. If anything, they were forging their own separate culture, then it's just back to a survival of the fittest match to see which side would thrive to control the rest of the Yeerks.
On the other side, I don't think you could even say Visser 3/1 could be classified as wrong or evil. Yeah, he was brutal and merciless and made it his goal to rule by complete force. He had to...did you see his competition? People looking to cut him down and take his throne at every turn, people who ATE other Yeerks had it out for him, people collaborating with the animorphs to take him down just for revenge. He had to do those things to keep his people in line. He would have never in a million years been able to keep control of Yeerk culture without such means, and even in the end it fell apart. If he didn't do it, someone else would have. That was just the way Yeerk culture was. Eat or be eaten.
If you think about it, that would be the only way you could hold such a society together. When you are basically becoming one with another creature, how long until you adopt their views and thoughts just from living in their head day in and day out? Not to mention you HAD TO live their life and their way. Visser Three had to basically hold together a culture comprised of seven or eight different races AND fight a three way war. You ain't going to do that by sending thank you cards. If he didn't rule the Yeerks with a heavy fist, his people would have fallen apart, and in the end that would have been wrong.
