I really don't want to put the question-asker on blast, because software is hard, and sometimes you're trapped in a quagmire and just need to fire out a question, but I'm not sure how many ways there are to respond to 'is it safe to push the button labeled "don't push this button, it's unsafe to push it, it's bad to push it, please don't push it, dear God just don't"?' Time is finite and some questions just aren't very good questions.
When I feel the need to contact developers about their code, I tend to think long and hard about whether them responding to my question is a good use of their time. I feel very uncomfortable making requests of others' time frivolously, and asking "is it safe to use this field in production?" would have made me feel as if I was making a fairly brazen demand to address what is ultimately a self-answering question. I probably would have spent some time thinking "is there something different and more useful that I can ask instead?"
In this regard, Dan Ambramov did a good job, as far as I can tell, of iterating and eliciting a useful, actionable feature request from the question-asker. He converted what could have been a negative interaction for both parties into something that potentially improves the project, and it's hard to ask for too much more.
I don't use React and I've never come across your name before today, so I think I'm a fairly objective observer. I would prefer that more people wrote like you do - clear, concise and to the point.
I much prefer the Russian approach. We are professionals doing professional work, our feelings are not part of it and if your ego matters to you that's your own problem. It is objectively stupid to use something named __SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED because, even if it works, you're not meant to use it! And they made it very, very, unmistakably clear. Dan did the right thing by not budging.
I didn’t get the impression from the reader that they were a beginner, or someone struggling, or someone who doesn’t “know they’re on the wrong path”. My impression was that a professional came to get an authoritative answer on a level of support of an API, and I tried to provide it.
I'm not sure it's wrong in this case specifically, because an answer to a question like "can I stick my fingers into a power socket" shouldn't be "I'm not sure it's a good idea and we don't support it, but you be you", it should be more like "hey, don't do it, you'll die".