A different angle is to look at what is accepted in a court of law. Laws do not consider copying/infringement to be stealing.
I know some people who say gunna (I was gunna do it). However, that doesn't make it correct. So, usage is not a measure of validity either. Most online dictionaries exclude steal/theft being linked to infringement/copyright.
Common usage does eventually lead to validity, though. Language is not static and evolves through usage. Besides, how are you going to measure validity? Is the OED the sole arbiter of what's "correct"? Common usage and mutual understanding is a great way to determine what's "correct" in a language.
I won't debate the legal usage of the word, as there was no mention of legal interpretation by the courts in the previous comments. However you are correct from a legal perspective where words have specific meanings.