Hashirama is not as clueless as some perceive him to be.
He is neither blind, deaf, nor stupid, though he paints this careless caricature of himself like he cultivates his forests, with broad strokes and sweeping hands.
Being underestimated is far more desirable than being overestimated.
He sees the corrosive nature of Madara's discontent. He hears the comments, the whispers, the judgment of the villagers. He understands that, at his core, Madara will never be satisfied with the peace that they've built. That, someday, the weight of his ambitions will crush Konohagakure. That, eventually, the leaves of memory preserving their tentative relationship and veiling the village from danger will be charred to ashes.
A fire burns those closest to it.
Perhaps I am stupid after all, he thinks, approaching this inferno of hatred he calls "friend", as he prepares to be scorched again.
Notes: Title taken from "To Those Who've Fail'd", a Walt Whitman poem.