I'm still confused. I am completely free to choose whether or not to do business with them, but I am not allowed to tell them about my choice? Or am I not allowed to speak about it at all, regardless of who listens?

Issuing threats is not free speech. You're still free to choose with whom you do business. Terribly sorry, but I don't know how to make it simpler than that. Good luck in your pursuits.

Ah yes, and of course whether or not something is a threat depends on intent. And who could be a better judge of intent than ... throwaway894345. Who I'm sure has an incredibly nuanced way of determining intent that doesn't boil down to "SJWs have bad intent".