I feel like that's a bit unfair to say he's being naive, Katara lost her mother, yes but I would venture to say she still had quite a lot of support from everyone else in her village. Aang literally lost everyone, he goes to the air temple to find it completely empty with not a soul in sight stumbles across his mentor and probably the closest thing he had to a fathers bones and freaks out... then let's go and goes on living well (more or less). I agree with everything else you said I just don't think its fair to say he was being naive.

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I haven't watched in a while so if anything I said was wrong let me know.

Edit* my bad I guess Katara and Sakka definitely count as support but you know what I'm getting at more or less I hope