The 1st amendment does not and should not apply to business matters. You don't even need to look far from the subject matter, Musk has gotten in trouble before over misleading tweets. I don't see anyone bring up the first amendment when discussing corporate fraud. Why is it that executives can be accountable to shareholders but not workers?
"does not and should not apply to business matters"
The problem is this: At what point does something become a "business matter"? And yes, I have opined that the SEC is playing with fire and possibly sowing the seeds of its own irrelevance with it's threats to musk.