Not only did he only save Hinjo so that the possibility of him getting that curse removed didn't disappear. Really, it only makes him unable to kill people within cities. For him to be that pissed, he must have been planning on killing LOTS of civilians since it doesn't really stop him from dungeon crawling. He saved Hinjo so he could continue killing innocents after the curse was removed. He killed GLG because he forced him to commit a quasi-good act because even with his rationing the very act of saving a life at all disgusted him.