Wow. Thank you for the very kind words, flowebells!
I'm sorry you got those scathing letters. Ouch.

The thing that hurt most about them was that they were scathing, no? Seems like in both those incidences their concerns could have been conveyed in a more civilized way. And that's key.
(Disclaimer, can skip: I am
far from having it together on this. It's the ideal I often fall very short of! When I get really PO'd about something, look out, because, well, hello rabid wolverine mode, lol!

It doesn't tend to produce a positive effect.

Fortunately, it's usually not being up in anyone's face. It's usually a loud, growling vent away from, that may or may involve objects in flight or violence against inanimate objects.

But if I can give it some time and calm down, it's usually possible to figure out what it was that bothered me about it. Once those thoughts are in order, they can be presented in a way that has a much better chance of doing good. Or I decide it's not worth it.)
As long as you present what you have to say in a logical way that is firm but considerate, you have a good chance of producing positive results.
It can be helpful to indicate you give them the benefit of the doubt without excusing them, being inappropriately apologetic, or even stating it directly. Perhaps as in conflict, "I" statements would be useful. Like, "I feel it would be more helpful if..." as opposed to ,"you should...". I tend to be inclined to say things like, "I don't know if you realize that xyz can come off as abc...". That would be an example of implied benefit of the doubt --acknowledging that it may not be their intention without excusing it. (If anyone could chime in with more professionally-based tips, better ways to say this or better examples, please do!)
I don't think it's worth worrying about him getting fired. It wasn't gross misconduct. It may be inexperience, a call for additional training in appropriate therapeutic attitude or technique. If he truly is just a judgemental butthead (fundamentally in disagreement with the tenets of therapy), they need to know. But more likely it is a case of needing additional training. (So the word "butthead" should be avoided, lol.

) Just lay out your experience and concerns, and move on to better things.
As tempting as it is to lash out, it's probably most constructive to realize that perceptions are very much in play here and procede accordingly.
Good luck!