Do I want to be around someone with a gun? (e.g. Starbucks scenario)
What if a guy with a live hand grenade in a box sits down next to you, and starts shaking the box? Do you want to be sitting next to him? No.
Why? Because he has an explosive device that can maim/kill people within 50 feet.
A gun? Same thing. Read all the Gun Fail diaries and know that if someone has a gun, there is a good chance of it going off, no matter how careful they think they are.
California has laws that say a gun must be transported in a locked box.
So, yes, if I see someone carrying a gun, or if I am at a public event/meeting where someone is carrying a gun, I will call the police.
And while I am on it, there ought to be laws to say you are liable for any damage caused by a gun you own. None of this "It was an accident that my gun went off, the bullet went through your apartment wall, and your child was killed/maimed; an accident, so don't blame me..."
End of rant for now.