Everywhere I've ever worked, you can tell any boss things they don't want to hear. What you have to do is do it respectfully. I've told directors and VPs multiple levels up from me that I thought they were wrong about something in large meetings. I said it to their face and respectfully, and that was fine. As long as you understand your place and don't publicly trash your boss, there's normally no problem.
The tweet in question here was... not that.
The second tweet had some more sass to it to match the tweet he was responding to, but it also wasn't all that bad. He points out the above in that Musk should be bringing these things up internally rather than publicly belittling his own employees with what appears to be incorrect information.
Giving feedback has higher risk and cost to it than it would otherwise be so why even do it?
While I'm not claiming it's an immediate crisis, I think it is and will continue to become a net long term loss for corporate American culture.
Musk is now teaching the world you can just fire people for saying anything you don't like without even a phone call, it will only make people more apprehensive to talk more freely.
I seriously don't see Twitter ever being able to hire a worker of any significant skill level ever again.
I do agree that it can take extra mental energy to translate "this idea is stupid" to "the downside of this approach is..." if you are prone to thinking in a harsh, cynical voice (I'm guilty of it). That is energy well spent.