[davidp]

With the GPL at least, its major clauses are aimed at restricting software from being incorporated into closed systems. I don't know if eliminating that control was what the GP had in mind, but it would be one of the perhaps-unexpected effects.

See also: Licenses that prohibit use for military purposes or other things the authors consider undesirable.

[userbinator]

Without copyright there wouldn't really be "closed systems" any more --- sure, you might not have the original source, but it also becomes legal to decompile and publish the results --- and as the cracker/hacker/security community has shown, source isn't mandatory for doing interesting things with software.

If anything, the loss of copyright would cause a great advance in reverse-engineering technology --- and also attempts at defending from it. IMHO not such a bad thing after all.