I know that none of us wants to encourage illegal behavior, and I beleive that if a store, or restaurant or other commercial location wants to ban guns that is certainly their right to do so, at least right now. Unless you are a protected minority, such as by race, ethnicity, gender, disability, sexual orientation, age, and probably some others than I can't think of right now, a business owner can discriminate in any way he or she wants to, including banning of firearms. Personally I don't want to give my business to any place that will not honor my 2nd Amendment rights and also who creates a target rich environment for the deranged and evil. My wife and I used to go to Buffalo Wild Wings often, but have not in recent years because of their corporate policy. Same for Ikea.
But sometimes it is difficult to avoid going somewhere where guns are prohibited, often by statute. Examples include Post Offices, courthouses, and schools (I attend one or more "grandparents day" annually and always feel extremely vulnerable if I am unarmed, but I do not want to refuse the request of one of my grandchildren to attend such an activity). For these type posted locations an individual has to make their own choice, whether to feel safe and carry despite the law, to not carry and thus comply with the law, or not go there at all regardless of other consequences (like not showing up for jury duty).
I would like to see the law require any location that posts to also provide a metal detector and armed security, so that I would be assured that no one else is going to be armed if I cannot be. Of course that might not help me if some thug who is 40 years younger than I am, and in better shape, decides to attack me. But merely posting, and taking no other steps, means that most law abiding citizens will not enter with a gun, but we all know that the criminal, by definition, will ignore the law to his advantage. And something tells me that if a store, restaurant or workplace had to provide security in lieu of allowing armed entry, and were clearly legally responsible for the safety of the unarmed in their location, we would see far fewer posted places.