"Theft by definition requires that someone is wrongfully deprived of their property."
So I must assume that you've never heard of "data theft", or "theft of services".
And as far as what "theft" is "by definition", then whose definition are you talking about? The one definition out of all possible definitions that most appeals to you?
"Schwartz (sic) seemed to think that academic work belongs in the public domain; most especially, academic work that was financed by the public. I completely agree."
1) As you seem to realize, not all of it was publicly funded, and how anyone other than the people who financed the research and, secondarily, the people who did the research, lost the right to decide what is to be done with the research that was the product of their investment of time, effort, money, and labor, I'd like to know. And more specifically, how did the right to decide what to do with that research devolve on Swartz and you?
2) You might completely agree with Swartz about academic work belonging in the public domain but if you think that that interests anyone but you, or if you think that that is enough to absolve Swartz of legal responsibility for his actions, then you do not really understand how the world works.
3) Here's an explanation of JSTOR by commenter Ian Johnston, on page three of this comments thread and which I am going to cite here because you seem like the kind of person would would not bother to find it and read it if I merely gave the url::
Both the article and the comments show a profound ignorance about JSTOR. It is not a publisher; it is a non-profit group run by a consortium of universities to make research papers available at minimal cost to the academic community - which effectively means to anyone with a university affiliation. That's not a cheap thing to do. As well as the storage and bandwidth costs, there is subscribing to current journals and negotiating access agreements with the publishers (who often are rapacious, I agree), and also the costs of scanning in older printed papers which would otherwise be extremely difficult to access for anyone not at an institution which subscribed at the time.
To access JSTOR, institutions pay a significant but relatively small annual fee. In return there are terms and conditions of service, one of which says, in effect "though shalt not download the entire archive and then make it available for free". Had Swartz succeeded he would have undermined the basis for JSTOR and made access to research papers, both now and in the future, considerably more difficult and more expensive. His beliefs may have been passionate and sincere, but they were also misdirected and stupid. (Note that Ian Johnston later disavowed the use of the word "stupid" in this post, but in my opinion, it is far too weak a descriptor in the first place.)