What is theft? I view it as depriving someone of a thing which is rightfully theirs. I do not, however, believe that creating something gives one a right to compensation when someone else copies the creation. The alternative is the idea that everytime someone generates something of value, he or she is entitled to be compensated by those who would enjoy that value. Therefore, we are stealing when we find a way to enjoy something another person has created without paying them compensation.
A sendup of this theory is here. It reveals the absurdity of demanding a right to be compensated for everything that other people may value.