The better word is "copyrighted". None of the restrictions of the GPL are any greater than any other standard non-licensed copyrighted work. The GPL simply adds to what you can do with a copyrighted work, it does not take anything away. So debated the poor use of the term viral if you will, but it neglects the primary point, this "viral nature" is not a GPL specific feature, but a copyright specific feature.
So it's silly to say that the GPL is viral unless you are saying it as an extension of the fact that any copyrighted work is viral. If you insist on using the term viral, simply apply it to copyright and the way it applies to derived works. Point the finger in the right place, at copyright. The GPL takes advantage of this feature of copyright law just like almost any other copyrighted work, especially proprietary software, does!