I recognized that in my initial comment as a potential criticism. I did so for precisely the reasons you have brought up. Why? Because I understand terms can have colloquial and technical meanings.
But this does not imply that we shouldn't call attention to technicalities, particularly if it's with respect to an issue one thinks is important.
However, you seem to be arguing that even a technical application of theft is applicable to IP. I don't know how to disagree with that without diving into tedious details about what makes "ownership" a viable concept in the first place. Kinsella addresses it in the source I cited in a previous comment. So I defer.
By the same token, the word "theft" implies different forms of punishment than "copyright infringement" when used by people in day-to-day life. Is this difference in actual usage less important?
> Well, yes... Supposing that IP rights should exist!
Well, of course. But we could have the same debate about property rights, so I could deny that "theft" exists at all, yet the language used to describe theft wouldn't change.