If software was only written in interpreted languages, if tools existed to manipulate binary executables with the same semantic detail that source code can be edited with, or if computing machinery was programmed using switch combinations that were published in books, such a requirement would not be necessary. The distributed form of the software would be complete, it would be the software.
But compiling source into a binary executable, whatever its practical benefits, is a form of obfuscation and a means of locking software to a particular piece of hardware. For those who would modify or move software that they have received it is an inconvenience that is major enough to hamper or prevent their use of the software. This is why the GPL requires disclosure, to protect the freedom to use the software.
So requiring source for published software is not an intrusion into privacy, it is not coercion and it is not unfair economically. It is a neccessity. The source code for software is the software, it is the only complete representation of the software. Disclosure of it is a necessary measure to ensure that the software is actually distributed. Otherwise binary executables become the public tip of a private iceberg of code that can impact on the private or public life of those that use it.
Private development and use of software should be possible. But it is important not to confuse my right to develop software privately with a right to prevent you using that software privately when I publish it. Your private use of my software is public relative to me but this is only a matter of perspective. DRM and binary executables make private use of software impossible; they make your private use of my software a public use of it. Their effects should be nullified.
For cultural works, private development and use of work should be possible and supported by licenses. The Creative Commons licences do not allow for this. Possibly the practicalities of this and the effects of the minutiae of copyright law mean that this does not have much effect in practice, but it would be good to have the licences acknowledge both a private domain of use of culture and when this domain crosses over into the public sphere.