I watched a History Channel special on the JFK assassination some time ago. In it, the presenters go over the evidence for a conspiracy, particularly the large number of entry/exit wounds. Using 3-D, time-synchronized computer models built from the time sequences of the several cameras which were filming JFK from different angles, they were able to show that the shots that we know were fired by Lee Harvey Oswald can quite easily account for all the entry/exit wounds with no mumbo-jumbo or massaging of data.
While it is still possible that there were other shooters, Occam's razor would lead us to conclude that such explanations are superfluous and, therefore, improbable. Possible, but improbable.
Because of my interest in currency, the Federal Reserve and the modern monetary system, I have been watching quite a few YouTube videos propounding conspiracy theories all the way from the 9/11-Truthers to David Icke and his shape-shifting, Illuminati alien-lizards. One common thread I find in all these videos is that they say many true things that really are unpopular today - but they draw conclusions that are highly improbable, at best.
For example, the Zeitgeist movie argues that 9/11 is just one of a string of conspiratorial events which have been engineered as pretexts to launch wars. In WWI, the sinking of the Lusitania was engineered by the powerful elite who, knowing the ship would be sunk by the Germans, scheduled its voyage anyway. Once sunk, America had an excuse to enter the war. In WWII, Roosevelt had advance knowledge of the Pearl Harbor attacks both from Australian intelligence sources and from the codebreakers who had broken the Japanese Purple code. In Vietnam, the Gulf of Tonkin incident simply didn't happen at all. And, in 9/11, the government rigged military aircraft with UAV technology and crashed them into the WTC buildings as a pretext for demolishing the buildings with pre-planted demolition charges.
Not one of these conspiracy theories holds up under scrutiny. However, there is still a striking pattern that reflects something that is true: the American government consistently uses national tragedies as a pretext for entering war. Instead of conspiracy, I would describe this phenomenon as a confluence of interests. That is, when multiple parties all want the same thing, they will independently move towards that goal. Those who are looking for a conspiracy are likely to find one wherever there is a confluence of interests. Since conspiracies are improbable (they happen, but not often, and even more rarely do they succeed), we should ask whether there was a confluence of interests as a result of the national tragedies which are responsible for launching the major US military actions of the 20th century?
I think the answer is yes. The government profits from war by expansion of its powers, reduction of personal liberties, increased tax burden and increased territorial holdings (whether directly or indirectly administered). Private, political corporations profit by manufacturing weapons, sometimes used on both sides of a conflict. But the international banking industry benefits most of all by public debt. As both sides enter a conflict, they need to generate money to pay for all the weapons they intend to build to kill each other with. In order to buy these weapons, they can raise taxes. They can only raise taxes so far before the economy begins to collapse, so they begin selling war bonds which are promises of payment to the bond buyer from future taxes. But once they have raised taxes as high as they can be raised and have exhausted the war bond market, and still need more money, they must turn to private financing. The wealthy men of the world have enough money to give entire governments loans. When they loan their money to a government, the government's repayment plan is through future taxes. Essentially, the government is selling promises of future tax payments to international banks in exchange for cash now.
Now, every businessman is looking to do two things: maximize his profits while minimizing his risks. In fact, there is a name for the product of risk and profit, it is called Beta, the Greek letter 'B'. Beta is really what businesses are trying to maximize. Many people mistakenly believe that it's all about maximizing profits. This is not true. Highly profitable ventures that are even more highly risky may be a less attractive investment than less profitable ventures that are much safer. Loans to large, well-established and stable governments do not have the highest profit margins, but they are very safe. It is highly unlikely that the citizens of the United States are going to stop paying their taxes. So long as we will be paying our taxes, we will also be paying back the debt which the US government has racked up in our name. If you are an extremely wealthy international banker with zillions of dollars worth of capital you are trying to put to use, loaning money to governments looks very attractive.
But to generate sufficient demand for government loans, governments have to incur massive expenses. Wars and welfare entitlements are very expensive. Wars also happen to be very unpopular - except after a major national tragedy. So, there is a confluence of interests between national governments, international bankers (and other very large business interests) and the public after national tragedies. This is why the conspiracy theorists see a conspiracy. There is no over-arching conspiratorial direction of history. If you are a zillionaire international banker with excess cash needing to be invested, all you have to do is sit back and wait for the next national tragedy. When it happens, you work with politicians who are eager to increase their territorial power, tax revenues, etc. to sell a war. If you can fund both sides at once, that's even better because it allows you to hedge your risk... just give more loans to whichever side you believe will eventually win. There is no conspiracy required to make this happen because, after a national tragedy, the public really wants to go to war.
Now, war is only half or less of the overall expenditures of the US government. The bulk of US government spending goes to entitlement programs of one sort or another. These programs are also incredibly expensive. Unlike warfare, it is really difficult to whip up national fervor for welfare. The most successful expansion of the welfare state occurred under Hoover and Roosevelt during the Great Depression - the Depression was capitalized upon by politicians and wealthy interests in exactly the same manner as other national tragedies. Welfare, like warfare, is too expensive to be funded by present-day taxes. If taxes are raised too high, they public will object to further expansion of the welfare entitlements. So, politicians turn to the same means by which wars are funded: inflation and public debt.
The welfare state provides a similarly smooth, steady stream of low-risk profits to the banking system which operates the currency. By steadily inflating the currency, the nation's central bank silently spirits money from the hands of savers into its own hands. No conspiracy is required - there is a confluence of interests because wealthy bankers need a low-risk way to employ their capital while a nation's citizens want welfare entitlements. No one has to be brain-washed to want free stuff.
I think any sane person realizes that such behavior on the part of the public is ultimately self-destructive. We cannot continue destroying property in pointless wars and subsidizing laziness indefinitely. We cannot continue spending our children's and grand-children's money without repercussion. Eventually, something has to give. It is easy to want to blame others for the mess, and conspiracy theories provide a convenient means to do just this. "The reason we have so many pointless, destructive wars is there is a global conspiracy of Illuminati bankers who are pulling all the strings and brainwashing everyone." BS. We just don't want to face up to the truth that we the people share an interest in warfare and welfare with the government and wealthy bankers. It's morally convenient to blame an elite.
The reason there is too much warfare and welfare is simple: we tolerate the existence of an organization with the power to make decisions and export the costs of its decisions onto others. No conspiracy is required for government to make irrational and destructive decisions because it does not bear the costs of its decisions. The President will not get in trouble no matter how much debt he saddles the public with. No member of Congress will ever be punished no matter how much of our children's and grand-children's money he votes to spend today on subsidizing laziness and government bureaucracy. The industry of financiers, industrialists and other private services which surrounds the fountain of government spending all has an interest in protecting and increasing the public debt, inflation and taxation. No conspiracy, just a confluence of interests.