Offering a copy written work for free, placing it within the public domain, when it was not yours to do so with in the first place is still stealing.
If I go to my neighbor's home and give away his television, furniture, clothes, he most likely will not be too happy with me. He would call the police and have me arrested for theft of his personal property even though I gave it away for free and made no profit from the act.
Would you not do the same if someone walked into your home and started giving away your belongings without your permission?