ok playing devil's advocate a bit here.. it is not your right to do anything on private property it is up to the property owner to decide those things you have the right to decide if you want to enter that property and follow the rules.Someone who is "pro gun", but wants to restrict the rights of gun owners in any capacity is contradicting, and closer to being an anti than anything else.
call it good business practice, think about it there are people who don't understand guns and the people who enjoy them and see the need to carry them and that is fine. the majority of the shoppers in that store would be uncomfortable to a certain point seeing a gun in public. (whether or not that discomfort is unjust is not the point) so those shoppers might choose to shop in a different place or place complaints. majority rules in retail sales.
in the logic above you would give up your career and unlikely but possibly lose the ability to provide food shelter and other needed things for your family to please a few people who want/need to open carry for whatever reason that is. (i enjoy open carry also but i cc when it makes more sense) open carriers are not the majority by a long shot in this state or even country.
the policy was adopted after an incident. much like alot of legislation that is occurring nationally and locally. one bill still being debated on the state level was created because of a member on this forum who really in poor taste and timing open carried a long gun in Portland, he may have been the straw that broke the camels back for open carry in this state.