It's not a theft at all.
For a claim of theft to be made, someone, somewhere, somehow must be denied property of some kind.
Piracy is infringement, and we have that word because the hard fact is nobody, anywhere, anyhow is denied property.
There is value, and all that, but it's not theft, and it's not simple.
In the case of say movie piracy, or music, some entertainment work, infringement can actually add value back to the creator by making that creator relevant and with that relevancy, a potential buyer of works. Bob likes a band, shares a track with Joe, who likes it and buys an album they would not have otherwise purchased if it were not for Bob...
In the case of a technology, someone learns how to do something other people would rather they not know. No party is denied understanding or property, unless one wants to talk about a physical instance of the understanding, but that's a side show really. The value is in the info, not the piece of paper detailing it, but I digress too.
Here's the interesting thing:
Once more parties have that understanding, and despite originators preferring they not have that understanding, all parties can gain from new understanding that always happens on top of existing understanding, and in the end?
That's how we advance.
Question is what is worth what?
It's not one of theft, but infringement and of what makes sense in economic terms as well as our overall development as beings.