Is there an archetypal myth in which a person does something really good to humanity, but contrary to common sense that says that he should be thanked and praised, he's attacked by those whom he helped instead? There's a lot of situations like that, when people simply don't want something really good, because well they are people. Like Nietzsche and his Zarathustra, who came down to people and started talking to them but instead they were saying he's a fool.
Looking over the Motif-Index of Folk-Literature and Aarne–Thompson–Uther (ATU) Index, I couldn't find anything quite like you’re describing. The closest thing I could find is ATU Type 160, “The Grateful Animals and the Ungrateful Man", but it's not a close fit. To summarize, in this type of folk tale, a man rescues another man and several animals from a life-threatening situation. The animals repay his kindness, and he prospers, becoming wealthy and popular. The man who had been rescued, however, frames his rescuer for a crime he hadn’t committed. The village turns against the innocent man. He is sentenced to death, but is saved by devising a ploy with one of the animals to do something helpful for the village to get back on the people’s good graces. He is able to return to his normal life.
So, again, this only vaguely resembles your criteria: a) he aids one person (but only one) who shows no gratitude in return, and b) his people do reject him, but then come to accept him because he ostensibly does something to help them.
Additionally, there is ATU Type 155, “Ingratitude Is the World's Reward.” These stories don’t have the precise elements you’re looking for, either, but they do contain themes of ungratefulness.