I think the key in understanding the GPL is to look at what is not seen.

Withholding source code via cryptography, obfuscation, or just not revealing it for a period of time is both legitimate and moral.  This is a critical component of expression, which is composed of both speech and silence.

Legally removing a modifier's right to silence effectively criminalizes a large number of possible business plans that would've benefited countless people.

So, how many killer apps have been made impossible by the GPL and other copyleft?  We can't really know.  Want to structure Wikipedia's data, add value to it, and resell it?  Sorry, you'll need to operate at a loss and offer your data for free because of Wikipedia's share-alike license.  The fact is, we can't see all of the awesomeness that doesn't take place due to copyleft enforcement because fear of legal retribution means that none of this awesomeness can exist in the first place.

I think also that people don't realize what the GPL does to create permanent code monopolies.  This would be much more equitable if the author were also bound to the GPL, but in fact one of the prime uses of the GPL is to prevent others from selling commercial licenses while retaining one's own right to do so.

An awesome microkernel, okl4, was licensed BSD and at some point switched to the GPL for recent versions.  The reason?  The GPL unlevels the playing field and allows them to sell licences while taking in contributions in both source code and testing from people who will never have a right to sell the software in the same way.

A note about public domain: sqlite is public domain and is distributed in every country on the earth.