"Until the back of my hand cracked against Quackenbush's face I had never pictured myself in the role of Finny's defender... But I didn't feel exactly as though I had done it for Phineas. It felt as though I had done it for myself."(79-80)

I think that he's slowly becoming more and more guilty that he hurt Finny, and more and more willing to put it behind him. Here, I can see him mad that Quackenbush was indirectly making fun of Finny by making fun of physically disabled people. If he's mad at this boy who didn't even say one word about Phineas, then he's obviously very sensitive about the subject. Gene wants to protect Finny because it was his own fault that Finny got hurt. It's almost like he never wants to see Finny be hurt again, even if it's just by some stranger that never did anything specifically to him.

What does Gene think of Phineas now?