With regard to Banning I would agree with you. But closing the OT forum is quite different. That's simply a business taking charge of how their site is viewed by others, not violating free speech or getting rid of people they dissagree with.
And your analogy is correct but with one stipulation: how one behaves in that grocery store while dissagreeing does give the owner the right to 86 them. I know, I've kicked out a few people myself for reasons such as being obnoxious, vulger and rude. :)

...... Kendra