I've recently posted the following comment on Chaos Guide:
"I've noticed that most "heroic" MC types aren't well-developed. They usually fall into two categories: those who are overly extreme and would die for a villain without a second thought, and the hypocrites. "
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Extreme:
An example of the above would be one of the most famous fictional characters: Batman.
His morals of "No killing" caused hundreds if not thousands of people to die.
You can say that he isn't obligated to help others, and I would totally agree with you. But from his stand point he doesn't think like that. I believe that he feels some kind of moral obligation to the people of Gotham city, this obligation caused him to become the heroic figure who would stand for the weak.
But this same obligation due to his extremely twisted sense of justice caused him to turn into a person who wants redeem everyone, and if you learned anything from "Chaos Guide" you would know that some people don't want neither can be changed to what you think is good.