I won't quote again just because this is turning rather long, but I'll try to speak to some of the issues that were brought up.
1. It is a fine line to pull out your gun and confront this person without being ID'ed as a LEO. With how quickly this particular case went down, as a betting man, I would've bet that if a civvie had a weapon out, he would've been taken out also. Obviously, this is a personal choice, but it would really suck to be taken out by cops when you're trying to do the right thing.
2. I would tent to disagree and say that my viewpoint is actually pretty broad. I would counter that it's pretty narrow to think that the majority of people who carry continually get training and put rounds through their firearm. My assertion is that those who do get them, rarely do any more training than is necessary, or at most are weekend plinkers. Let's face it, shooting anything other than a .22. or .38 can be expensive, even if you are doing your own reloading. I cannot state this for a certainty, but once again, given the odds, I'd lay money down on it. That being said, I have no idea what your profession is and how often you fire your weapon. You seem like a very conscientious firearm owner however, from your postings. I don't doubt for a minute that you know how to handle your gun (there's a double entendre there somewhere

). I would feel much more comfortable with CC's if in this state, not only were there annual certifications, but semi-annually, or even semi-monthly proficiency requirements that were to be met. Like I said, if the only requirement is to not have a felony, that opens doors to a lot of people who I don't necessarily feel comfortable with the "right" to CC.
3. You're right, it's a tough choice to act or not act. If somebody were in the same situation as the cop, I say do it. However, knowing the layout of Trolley Square, where the incident happened, the risk would've been huge - at least in my book. Also...now that I'm thinking about it....if let's say the cop were there and you were there, would you let the cop handle it as he's the "pro" or would you join in? Just curious.
4. I guess this is just one point where we'll disagree. I'm a pretty strong libertarian, and really would rather have less gov't involved in my life. There is no inalienable right to safety. There is a right to bear arms, but I probably interpret that differently than you do. Private property is private property to me. You can do with it as you please. Given enough reasons, gov't can compel owners to do things. Fine, that's established in case law. I can live with that. However, my take on it is as long as you're not discriminating against one of the protected classes (you used slavery as an example - race is a protected class) you can pretty much lay out the rules as you see fit. Don't like tinted windows? Ban them from your parking lot. Does it make sense? Not really, but hey, it's your property. If you want to lose sales, so be it. As far as an undue burden, rather than say a mall, let's take a church as an example. This is private property that has public access and is basically a monopoly. Most churches in this state have asked that firearms not be taken in to their facilities. I respect that. That probably puts an undue burden on worshipers who want to practice that religion but that's the price you have to pay. Which is more important in this particular case, your god or your gun? Let's say this happened in a church. Would you sue that church? I know I wouldn't.
Sometimes showing sorrow and empathy is enough. Not every tragedy has to have a lesson, just like not every TV show has to be educational or entertaining. In this case lives were lost, and that's tragic. Was any lesson learned to prevent it? There is no way to prevent random acts of violence. Statistically these are outliers that can never be charted or predicted. That's why they're random. Can we do things to try and help catch these people before they get to this point? Sure. Can we practice our responses once these events start? Sure. Can we prevent them? No. Maybe CC's could've saved a life or two, but from the timelime I saw in today's Salt Lake Tribune, 3 were dead no matter if we mounted automatic machine gun turrets on every corner.