I think you've missed something important here. Without copyright, those contracts have nothing to offer you, so why should you agree to them? Without copyright, you could freely use, copy, reverse-engineer, modify, and distribute any bits you had. That leaves you with no incentive to agree to a EULA, and numerous reasons not to.

Now, that said, a proprietary software vendor could force you to agree to various terms in exchange for a warranty or support, which would potentially allow proprietary software to survive for a little while in the enterprise world. But for all of us who don't mind voiding software warranties...

(Also, I think you've missed the huge impact of copyright on fields other than software, where the issue of "source code" doesn't matter as much. I'd count that as part of the "net win".)