An author (lawyer or not) walks a tightrope when he/she wants to write authoritatively.
From law professor Eugene Volokh:
People sometimes warn law students of the importance of careful proofreading and word usage, by saying that errors (or things that are perceived as errors) impair the lawyer’s credibility. I think there’s some truth to this, but the focus on “credibility” is a bit imprecise — it’s not that people will see the lawyer as dishonest, or likely to be factually inaccurate.
Instead, I think a good way of thinking about it has to do with authoritativeness. Here’s my sense of the matter, admittedly an impressionistic one rather than a scientific one:
Rightly or wrongly, something that seems to be a thoughtful written argument by a respectable professional tends to have more than just a logical persuasive effect — it also has a psychological effect. If the argument is well-crafted, the reader is inclined to credit not just the factually verifiable claims in the argument (whether about fact or about precedent), but the analogies and the speculation in that argument, too.
. . . .
As a lawyer, you want to create this bubble of authoritativeness, so you can take advantage of this psychological effect. But slips, even something as small as a typo, or something less small, like a usage error, can pop that bubble.
First, they distract the reader from the flow of your argument; they break the spell that successful rhetoric can cast.
Second, they make you seem less authoritative — sloppy (as with typos) or ill-educated (as with usage errors, or perceived usage errors). The reader won’t consciously say, “Oh, this lawyer doesn’t know how to use this word, so I’ll vote against his client” or even “so I’ll be more skeptical of his logical argument.” But subconsciously the extra support you’ve gotten from your perceived authoritativeness (whether or not that perceived authoritativeness is justified) will have largely disappeared.
. . . .
If you look like you’re angry, overexcited, strident, or even too impassioned you don’t look like the sort of person that we see as most authoritative any more. You thus lose the psychological force that the bubble of authoritativeness provides you, and you’re unlikely to regain that psychological force through your visible agitation or emotion.
Link to the rest at The Volokh Conspiracy