Store policy has the force of law, trespass law.
Not in Utah. URS 76-6-206 sets a pretty high bar for trespass in a place of public accommodation that is open to the public. It requires that entry first be "unlawful" and there is nothing unlawful in Utah about carrying a gun legally but in violation of the policies of a business open to the public. Having entered or remained unlawfully, a person must then intend to cause problems or commit crimes of some sort. Furthermore there is an affirmative defense against a commercial trespassing charge if the property was open to the public and the person's "conduct did not substantially interfere with the owner's use of the property".
It isn't even clear that a request to leave from a place of public accommodation for no other reason than the unwanted presence of a firearm would be sufficient for a commercial trespassing charge to stick. However, if asked to leave, leaving quickly and quietly and not returning with an unwelcome gun is all but entirely assured to prevent any criminal charges, much less a conviction. In 20 years of political activism in Utah I'm not aware of a single charge, much less conviction, for commercial trespass for someone violating a no-gun policy in a store, while actually going about his shopping.
Obviously, laws vary by States and in some States and under some circumstances (proper signage, for example) a private policy at a business has full force of law.
But not in Utah. In Utah there are only two cases where private gun bans have force of law:
1-At private residences;
2-Inside houses of worship.
In both cases "proper" notice must be given for the law to take effect. Proper is legally defined and for churches includes--among other more common options--being listed on one of our Government maintained webpages as having banned guns.
But business property, places of public accommodation enjoy no such benefits.
It is perfectly legal for me to carry into Costco stores in Utah. It is perfectly legal for them to revoke my membership if they discover me and want to do so. But even that would not necessarily keep me out of their stores. Under law, pharmacies cannot limit services to members and so are open to to everyone.
As gun owners and OCers, we are responsible to
KNOW the laws that affect us.
I've spent 20 years reading Utah gun laws, figuring out how to repeal the bad laws while strengthening the good laws, and even helping to craft some of the language to move us incrementally toward proper respect for RKBA. Feel free to ask questions. But it would be likely be a mistake for you to think you know more of Utah gun laws than I.
Now, if someone is just butt sore about some gun owners patronizing Costco despite a (generally) non-enforced gun ban, they should say so directly.
Charles