Most governments, and especially the American system, are just a conglomeration of competing interest groups. What benefits one group does not necessarily benefit the other. I have no faith in anything any government official says, but anyone who understands government bureaucracy knows that by nature big bureaucracies are slow moving, risk averse and generally make a mess of almost everything they are involved in. Bureaucracies and bureaucrats generally are primarily interested in expanding their budgets and keeping the bureaucrats employed. Because of this they generally seek stability.
That is why people with a decent sense of how the government works (or does not work) understand how unlikely it is that a large bureaucracy is capable of complex and risky conspiracies requiring participation and silence by hundreds or thousands of people.
Furthermore it is unlikely for one interest group (say oil companies or defense contractors) to be so powerful that their interests override the interests of competing interest groups (such as the airlines and the shipping industries which are equally large and powerful and who have been severly hurt by the increase in oil prices).
Most things that are being blamed on complex conspiracies and malicious intent (i.e. 9/11 and faulty Iraq intelligence) are actually the result of standard bureaucratic incompetence.
