meliorism (n.)

as a metaphysical concept, "belief that the world tends to become better or is capable of improvement;" in practical terms, "the improvement of society by regulated practical means;" by 1868, attributed to "George Eliot" (Mary Anne Evans), from Latin melior "better" (see meliorate) + -ism. Related: Meliorist (1835); melioristic.

In her general attitude towards life, George Eliot was neither optimist nor pessimist. She held to the middle term, which she invented for herself, of "meliorist." She was cheered by the hope and by the belief in gradual improvement of the mass; for in her view each individual must find the better part of happiness in helping another. ["Life and Letters"]

I don't know that I ever heard anybody use the word "meliorist" except myself. But I begin to think that there is no good invention or discovery that has not been made by more than one person. The only good reason for referring to the "source" would be, that you found it useful for the doctrine of meliorism to cite one unfashionable confessor of it in the face of the fashionable extremes. ["George Eliot," letter to James Sully, Jan. 19, 1877]