The only thing that you forget, is that if the employees ask you to leave, You must leave and by law, you're trespassing at that point if you don't leave. That's the only legal stance they have.
Same rules apply for Conceal carry of a weapon. It's not illegal to carry in the store that says no weapons allowed, but if they see you and ask you to leave and you don't, you're now trespassing.
The only thing that you forget, is that if the employees ask you to leave, You must leave and by law, you're trespassing at that point if you don't leave. That's the only legal stance they have. Same rules apply for Conceal carry of a weapon. It's not illegal to carry in the store that says no weapons allowed, but if they see you and ask you to leave and you don't, you're now trespassing.