All a business can do is refuse to do business with me.
We all know that statement is false.
What you meant is you can refuse to patronize a business.
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It's fine if the NBA -- or any private group -- wants to censor speech on its own property. People who attend games or work for the NBA agreed to abide by its rules. Likewise, Fox is free to fire me if they don't like what I say. That's the market in action, reflecting preferences of owners and customers.
But it's important that government not have the power to silence us. We have lots of companies, colleges and sports leagues. If one orders us to "shut up," we can go somewhere else.
Isn't this what you meant by refusing to patronize a business?