Kira acknowledges Setsuna's a very skilled pilot, but he's also concerned because dammit, this is a fight for survival, and if Setsuna won't use his talents and his mobile suit to help defend innocent people - not just on this ship, but in untold universes - then he's wasting his strength and only contributing to the problem. They can't afford to fight among themselves.

His obsession with the ideal of "Gundam" (which to Kira is just an OS acronym) is a bit off putting, as is his total righteous conviction that Kira and the rest are doing something wrong. Kira doesn't think he's beyond saving, though, and would still like for him to join their side.