"You should go through all the points. And you never answered the question. What laws or restricitons prevented OKC, prevented the anthrax letters, prevented presidential assassination, keeps thugs and criminals out of you house, prevent you being attacked on the street."
Ok, I did answer all the points you raised, at length, above. Now I will answer this last set of questions.
First I will answer it with a question of my own: what law ever prevented ANYTHING, completely, from happening? There have been laws against murder since the dawn of man. Murder still happens. And yet, when killing is made illegal, there is less of it than when the law is indifferent. Consider the case of duelling. Undoubtedly, there are still people who kill and are killed today, in 2007, in duels. But not nearly as many as were killed in duels in the 18th Century, certainly not in relative numbers, but also not in ABSOLUTE numbers. America has about 100 times the population that it did at the time of the Revolution, and yet it has perhaps only a hundredth of the total number of deaths through outright, intentional duelling as occurred then. When you outlaw something and punish people for it, it does not completely stop it, but it certainly discourages it.
The same is true of every other social disease and distemper. Do you imagine that ceasing to criminalize child pornography would leave the volume of it available untouched? No. The exploitation of children for evil purposes would explode. Were prostitution legalized, would there be the same amount of it? No. In Holland, where it is legal, statistics show that over ten percent of the post-pubescent males avail themselves of the services of a prostitute every month. Ten percent. There is prostitution in America too, but nothing like ten percent of the population uses prostitutes every month. However, in Las Vegas, where prostitution is legal, there is a tremendous flow of visitors for precisely that reason.
One can name any social distemper and find two truths:
(1) Outlawing it does not make it cease completely, and
(2) Legalizing it causes it to increase and the problems to expand.
Sometimes, as with Prohibition of widely-used substances, the effect of the law is to generate more criminality. Alcohol in the 1920s and Marijuana today come to mind.
But now let's turn back to your examples. Did the laws prevent the Oklahoma City bombings? No. But one need only follow the news carefully to realize how many bombing rings and terror plots we have broken up specifically because we now chemically tag fertilizer. Certainly if weapons of mass destruction were legal, they would be widely available: there is a market for these things. And just as certainly, Israel would have been destroyed by now. Similarly, 9/11 wouldn't have been four airplanes. It would have been 15 jihadis with their own personal atomic bombs. It is simply not true that there is widespread expertise in making WMD. But certainly if the stuff is LEGAL, it takes no great expertise to buy it and operate it.
Were the anthrax letters prevented completely? No. But the laws against biological weapons, and the tracking of the materials that could go into it certainly tamp down the ability of crazies to make the stuff.
Have Presidential assassination attempts been completely halted by laws against murder and heavy control of the President's area? No. And yet, for all of the attempts since 1963, none has succeeded. So yes, policing does make a difference.
I have actually never been attacked on the street anywhere in my life. This is certainly in part because of good policing.
Finally, there is a case directly on point. There are crazies in America who buy guns and go shoot up schools, Luby's, McDonald's, courthouses: it's true. There are drug gangs who shoot each other up. But you know what you DON'T see or hear? Machine gun massacres. Gangs going after each other with fully automatic weapons. The gun control of the most lethal mass-casualty guns HAS BEEN EFFECTIVE at keeping them off the streets. Machine guns exist, but they are damned hard to get. Criminals don't go to that length. They get pistols, and that is good enough for most of them. This limits the damage they can do.
So, on the one hand, it is true that there is not one law that stops completely the crime it is aimed at.
But it is also true that most laws, in a functional state, do DEPRESS the rate of violence and crime that would otherwise exist in the absence of the laws.