They didn't take it from the public any more than Led Zeppelin took their songs from the public when they sued those who violated their IP rights.

Software has a real and tangible value. Songs ... well, you decide their value, but I don't understand why the value songs create should be protectable, but software not.

That's really what this is about. This is about granting to those who write software the same rights to that property as anyone else who has rights to what they write.