Middle-child syndrome? He wanted desperately to excel? After what happened with Barty, it had to be difficult for Percy. He "backed the wrong horse" in the personage of the organization the Ministry of Magic. Honestly, I could see how he would do that. The Weasley's, for the most part , were law-abiding citizens! His father worked for the ministry. His blind belief in what his government is/was doing is something we see over and over again in the real world. Some do not question, they only follow. It doesn't make him stupid, just naive.

AHacker