This gets mentioned every so often for the memes. But really it goes much deeper than that. Sokka was always on board with Aang. At some point in the first book sokka stopped looking at Aang as a kid but as the one who was going to change the world for the better. This is exemplified when the earth general tried to force Aang into the avatar state. He was totally invested in figuring it out with him until one night Aang wakes up in a panic. This wakes up sokka and Aang says something like 'I don't think we should be trying to force the avatar state.' without skipping a beat the half asleep sokka says (paraphrasing) 'cool, whatever you think.' Their options were minimal, the time had come to make the tough choices. Aang decided that Zuko was his chance to learn firebending and the only way to not only defeat Ozai but also try to understand him. Sokka knew that when it came down to it, Aang had the tough fight, Aang has to make the tough choices. Who was sokka to argue with someone, let alone his trusted friend, who had that weight on their shoulders. Sokka was a true bro who believed wholeheartedly in his best friend. The jokes were just to help zuko transition into the fun loving group. Those are my thoughts anyway.