This sequence of events is amazing. Krona wearing 7 different lantern rings, Hal Jordan explaining why he continues to fight alongside the Guardians of the Universe despite their short-comings, and Sinestro helping out his former trainee and declaring that he also believes in the Green Lantern Corps.
Maybe it’s because Mogo is already dead at this point of the story, and the Green Lantern rings have no moral compass to guide them when choosing their new recruits. I still believe it’s because Sinestro risked his life to save Hal Jordan and admitting that despite forming the Sinestro Corps, he’s still a Green Lantern at heart.
From – Green Lantern Vol. 4 #67