"Wait," you're thinking, "I didn't say sell. I said give away!"
Ah, yes, but were you planning on accepting pull requests? Because exchange of money is not the only way to sell something. There is also the concept of "In Kind" payment (http://en.wikipedia.org/wiki/In_kind). So, you make a library with something like a WTFPL license attached. I download your library and use it for my product. Then, to show my gratitude, I submit a pull request with a new feature to one of your other projects (an "In Kind" payment). Later, I find that your first library has a bug that's causing problems for my customers...
...so I sue you for violating the Implied Warranty that you didn't disclaim in your WTFPL license.
This is why all of those open source licenses have the ANNOYING ALL CAPS clauses explicitly disclaiming any implied warranty.
The More You Know!™
So, as far as in kind is viewed by the state, software has been left alone.