You don't need a reason to help people.
Religion was invented when the first con man met the first fool.
A hug is worth a thousand words. A friend is worth more.
The death of a friend is equivalent to the loss of a limb.
A friend is one who believes in you when you have ceased to believe in yourself.
Yes, it's rather funny, really, that next to no-one realized the snake that Harry set free in Philosopher's Stone turned out to be Voldemort's final Horcrux, Nagini.