SCP Foundation

I'm guessing this is the writing of a relatively modern-era scientist, so the "confession" sentences feel overly stuffy at times, especially when there's still some casual language in there.

It's a subtlety of the effect (maybe I'm too attached to it): it doesn't make you blurt out thoughts exactly as they are phrased in your internal monologue; it gives you an urge to share what weighs on your mind, within the medium you're currently using. So the writer of the document would still apply their idea of technical writing. Clinical tone is not suitable to express intimate feelings, so casual language seeps through: I want the reader to get a feeling of the internal battle to follow the guidelines. I see I didn't really succeed, thanks for sharing that impression, I'll try to rephrase all "confessions" with that in mind.

For example, "Any information about SCP-xxxx is to be withheld from anyone except members of the SCP-xxxx research group: 0/xxxx clearance and any other Foundation-issued clearance are mutually exclusive." can be rephrased as "Information on SCP-XXXX is restricted to the SCP-XXXX research group, regardless of clearance."

The "mutually" is extremely important: no-one must learn about SCP-xxxx; AND xxxx-researchers cannot know anything else (because there's an increased risk they'd leak it). "Restricted to" does sound much, much nicer than my contrived "is to be withheld" though.

why is only one person writing the article?

That's addressed in the last paragraph: basically they picked a researcher with the safest possible set of knowledge and the most boring life (you can't leak anything important if you don't know about anything important, and less personal issues= less frequent confessions). Any new writer will confess whatever weighs the most on their mind, and thus double the risk of major leak. Did that annoy you while reading because a single writer felt wrong, or did you wonder about it afterwards? Would a short explicit instruction about it in the Special Containment Procedures feel appropriate?

Out of curiosity, is there a reason you have the "induce increasingly hostile behaviour in all subjects" effect as well? It's kind of an overused formula addition ("makes you crazy/angry/violent") and doesn't quite seem necessary.

I see the pitfall: "I want my murder beast to be even more scary, I'll add an epic 'rage state'". Here it's not an afterthought, it's just that the urge to confess doesn't go away, and if people are restrained to prevent confessions, the frustrated urge becomes unbearable. I'm sticking to the core cliché "this item is too good at what it does": if you can just cover their mouth and thwart the compulsion, it's a very inefficient compulsion… You've helped me see how sentences like that are trite though, I need to phrase it very carefully.

• internal conflict of a writer who knows he's under a confession effect, and tries to limit its disruptivity (but fails here and there, to give a sense that it's effective). Relies heavily on making the insecurities of the character believable and poignant.
• the idea of a booth that reigns over those who step inside, and for which "conversations about the booth" qualify as part of its insides. (I've never seen this explanation for the common gimmick "just talking about it triggers anomalous stuff": is this justification clichéed too?)
• the boring dork of the lab being assigned to this document, because everyone senses there's less risk he'll confess shady past activities or sensitive info. This strategy backfiring, because even someone as vanilla as him is full of alarming insecurities and resentment, and compelled confession triggers a "shame feedback loop": petty confession->shame about it->shame about people seeing that pathetic shame->shame->shame […]
• a confessional booth being a major threat for the Foundation. In itself, it's not actually evil: its victims are compelled to express what's on their mind, to let their internal struggles out (the unknown church that made it is not a focus, but if it were I would portray its intentions as the best interpretation of the Christian concept of confession). But within the context of the Foundation, this benevolent thing becomes a huge threat to information security.