That's the issue though. In 2011, in a suburb of Phoenix, I think it is silly to believe that carrying a gun while shoppping at big box stores makes you safer and that you should have a right to it
I'm coming from a place where I honestly do think it's silly to care a gun around when living a normal, suburban lifestyle in order to feel more safe. I understand carrying it in a bad part of town and especially having firearms at home or even leaving it in a glovebox, but having it while you go to Safeway and Target is a joke. Not a joke in the way that it's not proper fashion, but a joke that they believe it's neccessary to feel safer at Fry's. Plus, it's not like those signs are going to stop bad people from commiting a crime inside if that's what they set out to do.
Without going into whether the mindset is correct or baseless paranoia, gun supporters argue that you never know when a crime might happen. You might go to Fry's and get robbed in the parking lot. It doesn't matter that it rarely happens, the point is that it is always a possibility. In that sense, always having your gun with you is simply being prepared for the possibility that something might happen to you.
Your own sentence at the close speaks to that mindset: "Plus, it's not like those signs are going to stop bad people from commiting a crime inside if that's what they set out to do." That's the whole reason people who carry guns want to be able to carry them everywhere. They believe that having a gun on them will offer them some form of protection and serve as a deterrant to people who would try to commit crimes against them. Whether or not that mindset agrees with your own is irrelevant; that's what they are thinking when they try to get looser gun laws in regards to concealed carry, open carry and the like.
Personally, the more I'm exposed to guns, the more I think they should be legal. I used to be very anti-gun, but that's because I never had exposure to them, just exposure to paranoid PSAs which told me that every gun will kill me and my family members because it wants to. I'm now living with a veteran who has a small collection of firearms, and with exposure to seeing how guns work, I think the paranoia about guns in the general population is pretty absurd. I don't think that if everyone carried guns, there would never be a crime again, but I also don't see the need for extremely restrictive gun laws for people who want to carry them legally.