One commonsense point that many forget is that there are real, hge resources out there designed to do things covertly and mislead about the source. We spend many billions on the CIA and other operations for covert activities, and yet, many pretend that they don't actually do anything.
On the other hand, while that's a great argument for any given theory being plausible, it's quite another matter to say there actually is a conspiracy, requiring some evidence.
For example, just today I was reading some of the history again on the Nixon conspiracy to overthrow the elected, socialist president of Chile; declassified CIA memos show that many millions were spent over a long period to discredit the left and manipulate their political system. Over half the opposition party's budget came from US funding. More money was spent per vote by the US than the two US presidential candidates, Johnson and Goldwater, had spent in total combined in our own election previously. The US was paying to try to shut down the
Chilean economy, to prevent them being able to get any goods, paying for strikes - and then twisting the economic problems to 'prove' that the left's policies were bad for the economy. And the memos made clear that it was important that the fact that the US was behind all this had to be hidden from discovery, which it largely was at the time.
At another level, people who want to commit crimes are often guilty of conspiracies which are hidden as well. One of the most famous murder cliches is 'make it look like an accident'; logic suggests that many 'accidents' are disguised murders, often conspiracies, as many such attempts are discovered, and there's every reason to belive that many are not, as they're designed not to be discovered.
When Valerie Plame was outed in retribution for her husband's exposing the administration's wrongdoing, it was reasonable to suspect the more ruthless partisans had conspired to do so - i.e., the Vice President's office. George Bush talked at the podium about how concerned he was at this very serious misdeed, but said the federal government is huge, it could be any of thousand of people in many agencies, ad he said, with wishful thinking, it's unlikely to ever be found out who leaked. But to his surprise, the information was found out, and wasn't an anonymous person in the bureacracy far from the White House, but was a conspiracy in the Vice President's office.
When the administration was advocating war with Iraq, it was ot unreasonable to suspect them of exaggerating the case; later, it was found there was a conspiracy in which they would leak information to the media, and then cite the stories quoting them anonymously as 'independent evidence' that it wasn't just them saying these things.
But these things need evidence to be more than theories - even if plausible, even probable, theories.
The Iranian hostage crisis was a huge help to the Reagan presidential campaign; the hostages being released at the moment he was inaugurated could just have been coincidence, a 'goodwill gesture'. Or it could be the treasonous result of the campaign secretly negotiating with Iran to make it worth their while to keep the hostages and not cooperate with the Carter administration. The fact that the same people were found guilty of a variety of similar conspiracies, often illegal, and especially the fact that some involved secret deals with Iran on hostages, later added great credibility to the theories of conspiracy. But no 'smoking gun' proof has been found, and it's possible there was no such conspiracy.
Similarly, some research suggests that the 1968 Nixon campaign, with the Vietnam war greatly harming the democrats, secretly reached out to the government of South Vietnam and offered them incentives not to cooperate with the LBJ peace efforts - which they did not. Again, later proven conspiracies with the same players add credibility to the theory, but I'm unaware of it being proven.
To simply pretend that the theories are outrageous until proven is as or more wrong than rushing to believe them - again, pretending that the CIA doesn't exist is guaranteed to make some of your denials of conspiracies wrong, just as believing every conspiracy is wrong too.
The only way to deal with this, in my view, is to understand that the topic has to be discussed in terms of educated theories and possibilities, not blanket denials or endorsements.
I'm pretty convinced Lee Harvey Oswald was the only shooter at Dallas, and that 9/11 consisted only of planes, not pre-planted explosives. But I think we should discuss other possibilities, while demanding proof for believing them. One of the better preventions for conspiracies is to see them as possible and investigate, not to blindly dismiss them and make them all the more tempting, with low risks.
It's easy to forget now that during the lead up to the Iraq War, one of the reasons the WMD argument worked as well as it did was the public being conditioned to such info being accurate. Colin Powell's UN speech was made to play off the credibility of the JFK administration's UN speech announcing the presence of soviet nuclear missiles in Cuba, made by Adlai Stevenson. It's easy to forget how many citizens said things along the lines of 'they wouldn't lie about something so important', and how much cover that gave the administration to do just that. Similarly, that's a reason Watergate was so damaging, because Nixon played off the public's long-established trust that the president would not cross certain lines for politics, and they got burned for it.
I think the OP is indeed useful for reminding people that the phrase 'conspiracy theory' should not be allowed to be used as name-calling to get people not to consider the theories, which would just make it easier to get away with conspiracies. The fact that people will ask if the administration were behind a 9/11 attack makes it far less likely they would be.
