I think the point is that we should be more careful with the words we use. Saying that copyright infringement is theft is just sloppy thinking, and is likely to confuse the issue and lead to even more sloppy and confused thinking.
You might argue that both are wrong, that both are illegal, or whatever. Fine. Just don't say they're the same thing, because they're not.
Redefining words for purposes of brainwashing consumers is propaganda pure and simple, even if you believe that copyright infringement is wrong and should be illegal.