I don't know a source for the assertion, but I find it interesting and disturbing where things in general seem to be headed.

The legal concept of "theft":

https://dictionary.law.com/Default.aspx?selected=2119

"the generic term for all crimes in which a person intentionally and fraudulently takes personal property of another without permission or consent and with the intent to convert it to the taker's use (including potential sale)..." (see the link above for more)

So what does it mean to "take"?:

https://dictionary.law.com/Default.aspx?selected=2088

"to gain or obtain possession, including the receipt of a legacy from an estate, getting title to real property or stealing an object."

...and "possession"?:

https://dictionary.law.com/Default.aspx?selected=1555

"1) any article, object, asset or property which one owns, occupies, holds or has under control. 2) the act of owning, occupying, holding or having under control an article, object, asset or property." (again - more is available at the link)

Ok - so data can't be occupied, so we can drop that. Holding something implies that something is now in someone's hands and not in another's; data doesn't really work that way either. So - can you "own" or "control" data?

I'm not going further down this rabbit hole, but it seems to me that we have carved out this special exemption for data - or more generally IP - that isn't applied to physical objects. Which is to say that if you make a copy of data that isn't "your's" (whatever that means in a legal sense), that you have now, in some manner, committed theft. You have somehow stolen something from someone else - even though they still have theirs!

Imagine a physical item, and imagine you had a way to copy it. Maybe a wood table, and you are an expert woodworker. You see it, you take some measurements first, plus some photos, maybe a 3D scan? Or you used photogrammetry from the pictures to gain the 3D data. Whatever. Then you go home and make the copy in your workshop. You make an "exact" copy of that table, and the owner (the guy who originally made it - maybe he was selling it, too) learns about it.

Have you just stolen from him? Have you committed theft?

In the real world, if you tried to bring such charges, you might be laughed out of court (unless he had a patent on it, and you were trying to sell that copy - because patent law allows one to make such copies in order to make improvements, but those copies can't be sold or manufactured in quantity).

But when it comes to data - all of a sudden, it's different. With data, the deprivation (even if you are just keeping it for yourself, with no intention of passing it on to someone else!) is considered to be "a loss of sales revenue".

So why not in that case of that table? Or any other potentially manufactured artifact?

The "slippery slope" argument might be the idea that in the future, that yes, if you happen to make an exact copy of a manufactured article (whether manufactured as a singular item or by the millions, whether done by hand or by machines), and regardless of whether you intend to sell it or keep it for your own use - that if caught, you will be deemed as having committed theft; as having stolen something.

I mean - why not? That's what we do with data, so why not physical items?

The next step is, of course, to just define stealing or theft as being the deprivation of sales revenue...but that would be crazy, right?

As crazy as thinking that one could define stealing and theft as being something you do where you don't deprive the original owner of anything...?