I probably wouldn't think that Rorshach is an INFJ if I imagined INFJs as cute and fluffy creatures, would I? The problem is, Light is a cold mastermind in heart and doesn't really Fe even those close to him. Rorshach is mad. Before something inside him broke because of the murder of the little girl, which is something he couldn't bear due to his empathy, he didn't even want to kill the criminals. Also, I haven't noticed any real mastermind tendencies in him. He only does what his morals tell him, plus he's paranoid and his plans don't ring Te, as Kiras do. He's also morally absolutely uncorruptible, which can be hardly said about Light.
By his own dark ideals, Rorshach is indeed incorruptible. So is Kira. Has Kira ever not been true to his vision?