I get what Cloud's trying to to express, it's just that the statement he uses is actually quite silly.
He isn't fighting Sephiroth because he hates him, or because he needs to avenge Aeris. He's fighting Sephiroth because he needs to be stopped, and nobody less emo was available, who could do the job.
Remember, Sephiroth and Cloud were Shinra troopers from the same unit, even though cloud wasn't a true SOLDIER, and Cloud had tremendous respect for both his commanding officers. To see the heroic defender of his country reduced to an obsessed revenant, twisted by Jenova into a heartless killing machine, must seem pathetic indeed.