Even before Kyle, they were arrogant and condescending because they had centuries of experience telling them they had *reason* to be - they mostly were smarter than anyone else, and while they weren't necessarily more virtuous on an individual level, they had taken on the responsibility of protecting the entire galaxy. They didn't fuck up often, and when they did, it was stuff that no one else would have gotten right either. What advanced society, used to technology doing what it's supposed to do, could have anticipated a machine that metes justice screwing that up? And the Guardians' response to the Manhunter failure was to acknowledge it, learn from it, and put their *own* personal power on the line instead - every ring handed out makes the Guardians weaker. That's the kind of thing that will make you a little full of yourself, given time. And even then, they knew enough to be flexible about it like with the Hippie trip, to have contingency systems in place for when they screwed up again like with Sinestro (can you imagine the Johns Guardians' reactions to being told they gave the wrong person a ring?).
They've turned from guys who occasionally behaved as if they could do no wrong to guys who genuinely can do no right. And it is, as you say, extraordinarily adolescent.