Upvoted for precise thinking.
I agree that part of the problem with "if it can be known" is that "if it be known" is strictly superior.
On the other hand, an important fact in the critic's argument is that the consequentialist agent knows that strategy Y leads to horrible consequence Z. If he is simply unaware of this fact (but "it be known" by other people), then we would be entirely unsurprised to see him choose strategy Y - he is still a consequentialist, just a misinformed one - so no argument materialises.
Therefore I think that the use of active voice is clearer in this instance, because passive voice obscures the distinction between our knowing that strategy Y leads to horrible consequence Z, and the hypothetical consequentialist in question knowing this. Admittedly this distinction is not difficult to infer in the original piece, but numerous small inclarities can add up to make tedious prose.
On reflection, what you have said about the passive voice in general is true. Misuse of the passive voice to obscure agency when agency is politically or socially important is Orwellian; passive voice in general does not necessarily obscure anything.
I've written quite a lot here since Less Wrong started up, but I've started to suspect that my writing style is holding me back. Most recently, I wrote two sequences that seemed to garner widespread agreement on content/significance/originality but didn't really seem to excite anyone, which is a pretty clear signal that my style has been hobbling my ideas. So, as I'd promised to do (albeit a few weeks later than I'd expected), I'm trying to improve myself as a writer, and I need your help.
I'm declaring Crocker's Rules on the subject, and I'd like help with both diagnosis and treatment. Let me know, as precisely as you can, what's problematic in my writing, or what you think the root causes might be, or what you think might help me to fix my issues. I'll list what I've thought of so far in a comment below (so that you can make your own suggestions without anchoring issues).
Links to my recent major posts:
Consequentialism Need Not Be Nearsighted
Qualia sequence: Part I, Part II, Part III
And now an odd counterexample: I wrote this post quickly for Discussion, without thinking too much or editing at all, and then it got promoted and was received enthusiastically. That may just be the subject matter, or it may signify that the time I spend editing posts makes them worse...