Well, since we don't any of the Avenger's use Tony's gauntlet for a single stone and only for using all of them at once to "snap" I just kept thinking why not use just use the stone individually against Thanos.
Even using a single stone would have probably killed Tony. Normal humans can't use an infinity stone, which was made clear as early as guardians of the galaxy 1 when the collectors slave exploded on trying.
Tony might as well go all in and use all 6 for the instant effect since that's the case.