If biker clubs were allowed into Twin Peaks, that was the owners choice and he has to live with his decisions. You seem to think that choice should only be by those that think like you do.
From what I can tell, the owner of the restaurant promoted the biker event. Which, like you say, is his right to do so. Now, if he had reason to believe that it might turn violent and did not take precautions to reduce that risk, then I imagine that might be found out in a lawsuit.
I hope that a reliable investigation is done on the shootings. One gal that knew several of the bikers said over 30 guns were drawn and a hundred rounds fired. It was implied that it was the bikers doing most of the shooting.
I’m guessing that there will be videos of it all.