I really feel like sending a memo to my department chair but (a) this is Saturday, (b) it has not been solicited, and (c) everyone else has apparently written related memos this week and I doubt one more, no matter how good, true, or beautiful, would be helpful.
So I will publish the main points here, in preparation for saying them at any meeting which may take place.
Dear Co-Chair [seasoned faculty member], with copy to Chair [new external hire],
I told New Faculty Member three things over lunch last week and it occurs to me we might let Chair know them as well, since ze is also new. Here is what I told Faculty Member:
1- Part of the reason for the belief that at least some [students of X description] need preparation before taking Course Y has to do with the way this course was formerly taught, which involved shaming for any mechanical errors. It is no longer taught that way and errors are expected in all undergraduate courses.
2- Our program has changed in many other ways over the last 10 years. We have a new, differently calibrated diagnostic exam, a new, different lower level method, and a new, different upper level program. Also, the university no longer insists students “account for” skills building courses at beginning levels if they pass intermediate or advanced level courses in the same subject.
3- The reason so many people who were actually overqualified for Course X “needed” it 10 years ago as preparation for Course Y was that we were so perfectionistic about mechanics in all freshman, sophomore, and junior level courses as well as on the diagnostic exam. We have changed.
I am not sending this memo, as I say, because I have reason to believe it would be inflammatory. What do you think of my tone, though? Tempers are running very hot on this issue.
Axé.
coldhearted scientist وداد 
To me, the tone seems neutral and matter-of-fact. If you added footnotes (see here for our new methods) it would be positively scholarly.
Yes, the text appears that way and would be meant that way. But now is a good time to be really careful.
It sounds like a reasonable memo to me. All you’re doing is restating positions that the department has already agreed to. I know what you mean, though: if you’re talking to someone who’s irate, hearing reasonable truths or being reminded of history will just make ze angrier.
In the end I wrote something even milder. I want to say much more. I want to say:
1- If a junior level course in Spanish for business is so basic that it is not appropriate for native speakers, maybe that material could be covered in sophomore level conversation.
2- If students are getting 16 hours of credit for a 3 hour “heritage speakers” course when really they are native speakers evading the language requirement and the legitimate alternatives to it, and if this is happening so that the heritage speakers course will make, perhaps the course is not necessary.