translation.en: for principled reasons, he must have some corrupt, nefarious reason" — they're saying a lot more about themselves than they are the target of their accusations, because —  — those people, the ones who make that accusation, they themselves never act for any reason other than corrupt reasons, so they assume that everybody else is plagued by the same disease of soullessness as they are, and so that's the assumption.
translation.zh: 出于正当原因 他肯定有什么腐败或者不法的意图 他们其实更多的是在说他们自己 而不是他们指责的对象 因为 那些做出这些指责的人 他们自己才只会出于腐败的原因做一些事情 所以他们才会假设 所有人和他们一样 都受卑鄙无情这种疾病困扰 这就是他们的设想