That's the rule for public property, but I don't think it applies to private property. I believe that Costco can generally allow the Guardmen, Salvation Army, etc. to do their good work on their property - and still prohibit other groups.
If it was private property, then they would be expected to get PERMISSION to distribute flyers first.
The company can give permission to any group they wish on their own private property. The do not wish to support the National Guard that is fighting to keep this country free and that would be called out to help their sorry butts in time of a disaster. They are unpatriotic and should not expect patriots to spend money in their stores. Is that simple enough for everyone?