Moving out of your parents home and pursuing a career you want and placing trust in people who are not your family does not mean betraying your family.
Percy believed what he was doing was right. He believed the Ministry was correct. He believed his family was incorrect. Why place blind faith in a single teenage boy when there was a government to look to?
Mr. Weasley accused Percy of spying. He resented the accusation and moved out and did what he thought was best.
Just because he happened to be wrong does not make him a bad person. He’s the best older brother ever. Remember how proud he was of Ron for earning house points? He stood up in front of everyone and clapped. Remember how he was the only person to know there was something wrong with Ginny, and took care of her all through CoS? Remember how in GoF, even though he knew that Ron and Fluer’s sister were safe, he jumped in the water to help Harry pull them out, anyway, because he was too nervous about their safety? He’s a great boyfriend, too. He didn’t even care about his perfect scores because he was too busy writing Penelope. And when she got petrified in CoS, he was absolutely horrified.
I sincerely doubt he was fine with what was happened with the muggle borns, either. But when you’re already knee-deep in a sea of shit, you have to wade through it before you reach the shore. Which he did. And after being estranged from his family for three years, they reunite for all of a few minutes before Fred dies right in front of him. His brother. His little brother.
And saying he should have died instead of Fred is totally unfair and pretty terrible. None of them deserved to be murdered, and none of them are more deserving of untimely death than the other.
Appreciate Percy. He’s pompous and silly and adorable and sweet and placed faith in the wrong people. So did Snape, Dumbledore, and Draco, but nobody hates them half as much when they’ve done worse things than Percy ever dreamed of doing.