He who receives an idea from me, receives instruction himself without
lessening mine; as he who lights his taper at mine, receives light without
darkening me. That ideas should freely spread from one to another over the
globe, for the moral and mutual instruction of man, and improvement of his
condition, seems to have been peculiarly and benevolently designed by
nature, when she made them, like fire, expansible over all space, without
lessening their density in any point, and like the air in which we breathe,
move, and have our physical being, incapable of confinement or exclusive
appropriation.
Thomas Jefferson
He was talking specifically about patents, but the idea is still relevant for copyright.