As much as I think Sterling did a very stupid thing, you still can't take property in this country for something a person says. Plus what he said was obtained illegally. Sterling (or whoever represents his interests by the time this is over) is going to win in the end.
1) They're not taking private property. They forced out a business partner, and he was able to sell on the open market for $2 billion, which was certainly a fair price, if not an excessive price. Business partners force each other out ALL THE TIME in THIS COUNTRY, for a variety of reasons, including speech.
2) If his words were truly obtained illegally, he has recourse. He can:
a) press criminal charges
b) sue Stiviano
c) sue TMZ for releasing what they knew to be an illegally recorded conversation.
He has pursued none of these options.
The NBA merely reacted to the fallout.