I think people are really missing the point as to what copyrights are, and why we need them. The "Happy Birthday" analogy doesn't work, and Disney's stories may be based on old ideas, but are original pictations & dialog.
"
Copyright gives the author of an original work
exclusive right for a certain time period in relation to that work, including its publication, distribution and adaptation, after which time the work is said to enter the
public domain."
Basically, everybody has the right to a work...eventually. You can't own ideas or even inventions...you just have the right to use it exclusively for a time period that law dictates.
Get it?