Wanting to defend his homeland and believing that he might now have a chance is not being "corrupted by power". At a stretch you could argue it's hubris, but even then you're on thin ice.
Well first off none of the commanders really need to go off and fight. They've promised and staked their honor on that they will, but Agamemnon in return has promised them loot.
During the Bronze Age there was a definitive tension between chiefs and their king, much like modern street gangs today. Displaying weakness can lead to being overthrown, which is why all chiefs react so strongly to having their honor slighted. It seems almost disproportional today, but back then it was extremely important to keep in power. Insulting someones honor, by talking down to them, stealing from them, etc. can be likened to modern times by a country not respecting another's air space. Sure, it's not an invasion. They're not going to war, and generally it doesn't have THAT much of an impact. But it's a statement. "We're stronger than you, you can't stop us.". That's what Agamemnon did.
Achilles has been raiding the cities and villages around Troy during the war, and have given much of the spoils of his work to his king. In return he will demand that he is treated with respect, and the fact that he is the best fighter among them is recognized.
When Agamemnon takes his prize, and not only that, adds the real insult to injury by saying he is the better man, how much greater he is than Achilles he has committed the worst offence one chief could unto another. That's why Achilles considers escalating the conflict (and make no mistake, their verbal exchange is very much a conflict, since Achilles is now actively questioning Agamemnon's ability as leader and king) to violence, and killing Agamemnon. Only the intervention of a literal Goddess stops him, that's how powerful the slight to his honor was.
That's also the reason that when Odysseus tries to convince Achilles to come back and fight, after listing all the gifts Agamemnon will give him, he leaves out the last crucial part, about Achilles having to bow down to Agamemnon, and admit how much greater of a man he is. That's why Achilles insists that those gifts aren't what's going to "pay him back in full". He's not interested in money. He's interested in getting his honor back.
Here's a talk comparing the social structure of the Iliad to modern gangs. He goes more in depth than what I can in this post.
youtube.com/watch?v=XD0FEcK9smE