Background checks revolve around the concept of a list of people determined to be "prohibited persons," based solely on the assumption that such people are more likely to commit crimes involving firearms. While originally this discrimination started with convicted felons, it has since spread to include people convicted of misdemeanor crimes of domestic violence, people who have been institutionalized for mental illness, and people with current restraining orders against them. The current push is to "close the [so-called] Terror Gap," and prohibit the purchase of firearms to people merely SUSPECTED of being involved in whatever they define as "terrorism."
So we know from experience that a prohibition simply doesn't effect those willing to break the law - they will continue to get their guns, either with straw buyers, or steal them, or get them from the black market on the street. So what's wrong with making it harder for dangerous people to get guns?
First of all, with the wide variety of felony crimes our society has created, many of them victimless, a good many of these felons are NOT a danger to society, even if they have firearms in their possession. Consider some of the famous examples: Tim Allen (comedian) has a felony conviction for drug possession. Martha Stewart has a felony conviction related to her illegal stock trading. How is our society made better for prohibiting these people from possessing firearms for any good purposes?
While there ARE many convicted felons that really are a danger to society, if they are willing to disregard the laws prohibiting them from hurting innocent people, they're going to disregard the laws that prohibit them from having a firearm if they really want one. The only felons effected by this prohibition are the ones that choose to obey it, and the facts prove the ones obeying the law aren't the ones we need to be concerned about.
For individuals convicted of misdemeanor crimes of domestic violence, I actually know someone that fell into this category. My acquaintance Pete was living with his girlfriend when they got into an argument. He is well over 6' tall and she was over a foot shorter than him and less than half his weight. The argument got physical - she started the attack by jumping on him, knocked him over, and began flailing at him with her fists. He grabbed her, threw her off of him, and she hit a piece of furniture, causing a scrape and bruise on her back. He called the police to report the attack. When the cops arrived, she denied ever striking him and played the "poor abused girlfriend" sob story. The cops looked at him (with no visible signs of injury), looked at her bruise, ignored his side of the story and arrested only him. In spite of having a lawyer, the judge did the same thing, looked at the size of him, the size of her, believed her lies and convicted him. He has now lost his right to keep and bear arms under Federal law FOR LIFE unless he can get the conviction overturned on appeal (which he doesn't have the money to continue to fight), or gets a pardon from the governor.
Now I wasn't there, of course, so I only have the word of one party involved, but this kind of thing DOES occur. I also know people that have had restraining orders filed against them maliciously by an angry ex-wife (used as a tool to guarantee her custody of the kids), and that the prohibition of people with current restraining orders against them results in the restriction of people's rights without even being convicted of a crime! We know that truly dangerous people with restraining orders against them will break the law to go attack and kill their target, and sometimes they even use a gun - how is this prohibition supposed to work again?
The push to prohibit "suspected terrorists" is even worse, because the list is "secret." You have no way of even identifying IF you are on the list, WHY you are on the list, and removal from this list is next to impossible. It can result in people's rights being restricted with absolutely no due process, no convictions of a crime, and basically no redress. Those that really are terrorists willing to harm people won't be stopped by a simple law, and if they are denied their purchase, they may even realize they are now tagged as "suspicious" and change their plans to evade further suspicion.
Any of these prohibitions ONLY effect those who are willing to obey them. Trying to determine who is "dangerous" by these factors alone is a gross abuse of government, and in trying to protect us from these "prohibited persons" possibly abusing the right to keep and bear arms, they prohibit the good and rightous exercise of it. We throw many of these prohibited people who are NOT dangerous under the bus, in an ineffective attempt to prohibit the dangerous ones from getting guns, which doesn't work.
Either we all have equal rights, or we don't. We ALL have the equal right of self defense, and that means the equal right to an effective means of self defense of our life and liberty - This is the root behind the right to keep and bear arms. All people have this right, even if our government enacts unjust laws prohibiting it.