A semi-auto fires one round for each press of the trigger. A double-action revolver has the same effect. There are tens if not hundreds of millions of such semi-auto guns in the USA. If someone breaks into my house whilst I or my family are inside, they can expect a swift response from a 12 guage shotgun. They are not a target, but a violent criminal intent on something other than tucking me in and kissing me goodnight. The chances of this happening? Very slim in the area I live. But I chose to be prepared. In other, less well to-do suburbs, it may be a nightly struggle to stay alive.
Perhaps you are confused with full-auto/select fire guns, which have been banned in most forms in the USA since 1967 I believe. Now keep in mind, this doesn't stop the drug dealers/gang members etc from procuring their very own sub machine guns and pistols. They don't get licensed with the state, they don't have an FBI background check, a mental health check, the checking of references etc. They don't care about the law, they are criminals.
Unless you live in a very rural area, open carry by citizens can cause a degree of panic in the populace . Generally you would only see open carry by uniformed personnel (police, SWAT, security etc). The beauty of concealed carry is that when a violent criminal is in an area where he knows there is a good likelihood of their victim being armed, he doesn't know who in particular is carrying. Coule be Ethel the grandma at 70 years of age, or Bob the gas station attendant at 25. So those who choose to take on the burden of concealed carry make the streets safer for all. The idea that the only people who carry concealed are those itching to slaughter someone in the street is a little fanciful, can you show men even a singel news article where someone legally carrying a concealed pistol used it in a manner that was found to be illegal? Tens of millions of US Citizens carry each and every day. No innocent lives are lost, in fact many are saved by either the general deterrence of an area allowing carry, or the ultimate deterrence when the previous "victim" instead turns out to be someone who can fight back.
Compare this to the tens of millions of drivers that get in their cars/trucks each day. 50,000 or more of them each year don't make it to where they are going. You don't ban cars because a certain population cannot drive sensibly. You take away their license, and if they are really out to lunch, put them in jail.
The criminal would rather attack the weak, so he is more likely to commit a crime in an area where he knows that all citizens are unarmed. The inner city areas of many larger cities being a prime example.
We now have multiple school shootings. You cannot carry concealed in a school building without the administrators permission, so chances are no one is carrying concealed. The nutjob psycho students can walk in with heavy weapons, and slaughter children as they cower under their desks. We don't live in a police state, there isn't a cop at every corner. Some choose to take on some of the burden of safety for themselves. I see no reason to deny them this advantage against the criminal element.
The lethality of any weapon is directly related to the mindset of the person operating it. A butcher's knife can be used to carve a turkey, or kill a person. The human element is the sole distinction. The knife is a tool, just like a gun. And yes, there are groups that would like to see sharp pointy objects banned as well.
Anyways, I'm sure we will never agree on gun control, but I thought I would put a little perspective from the other "nutty" side