Possible reasons why governments have been trying to cover up UFO cases and evidence.

When I was doing reading and comprehension exercises on main themes of short articles at a school back in 2001-2002, I came upon a short article on my list about Alien & UFO Phenomenon in the 1940s-50s and how Science Fiction soared in popularity.
According to the article, fictional stories about visiting aliens were taken seriously and broadcast in radios all over.

One radio broadcast in particular that was mentioned in the article gave out a false alarm in the 1940s, causing a city-wide panic. And though the news broadcast, repeatedly stated this alien invasion alert was false (the article highlighting this factor), people completely ignored the radio and still were in a state of panic.

This interesting article, made me think of all the alleged UFO cover ups that the American government has been allegedly involved in. We read about them all the time in magazines, books, websites, articles (search UFO cover ups on google) or in The X-Files.

I started to ask myself, is this the reason why governments, the American government in particular? To avoid mass panic created out of false alarms, hoaxes and rumors?
If so the answer makes total sense.
For a long time hard-core believers have been coming up with UFO stories without proof or evidence, sometimes accusing government of collaborating with aliens to control the human population.

From the point of view of the CIA or the American government, to try and hide physical evidence that would lead to these false alarms & rumors by those with the intent of manipulating this physical evidence to their advantage.

So let's suppose an alien spacecraft crashes on Earth. What could that mean? Hardcore believers & conspiracy theorists might scream "look aliens are coming to invade- look at the evidence: a wrecked spacecraft" when the reality might be the spacecraft belonged to peaceful explorers who had nothing to do with the government. Perhaps the craft never even intended to land on Earth and simply got caught in our orbit, causing it to crash. There could be countless reasons. Who knows?

But the point being, that because this has caused mass panic in the past, leading to false rumors, the US government might be doing what it sees right in preventing further damage being done by false conspiracy theorists.
At least this could be the explanation from their point of view.

What if alot of wrongly perceived "UFO crashes" like The Roswell incident is all the remains of a human-made craft. The claims of the debris being an alien spacecraft or probe could be set off by bored people looking for an adventure or people who actually believe it's a UFO crash because they cannot properly identify the vehicles components.

According to a UFO book I've been reading at my local bookstore, Mac Brazel, a key witness in the Roswell incident, was detained by the US military for a week.
After all, he also possessed the wreckage of the alleged spacecraft. What if his finding was simply a misunderstanding and led to what could become a widespread panic amongst the American population, or even worse, a spread in false rumors that would lead to turmoil, hence he was ordered into silence by the military during his detention.
Reports have indeed stated that he was not willing to speak of what he saw or knew about the alleged UFO after his detention.
This is what it could be all about.

This could be the whole reason for government attempts to silence/deny UFO cases.
And even if there is a case(s) of real UFO crashes on Earth, who could possibly know that the crash remains could be dangerous material, perhaps radioactive or composed of other substances dangerous to life on Earth.

Allowing a UFO case to go public would only lead to curious people exposing themselves and perhaps spreading dangerous diseases or other hazards from the UFO & alien remains, forcing the government to keep it silent, until they can guarantee, they pose no threat to Earth's population.
And let's not leave out the spread of false rumors. Though I am no skeptic and believe in life on other planets, I am not ignorant to the fact how many people and news agencies out there exist ready to exploit & exaggerate real or fake cases of UFOs, for fun or for profit.

And if my theories are correct, the government of America and of other countries around the world are justified in keeping these incidents secretive until they can fully guarantee these UFO wreckages/alien corpses pose no threat to the population.
Let's not forget the government's first responsibility is the interests of the people.

Though I also may endorse certain government attempts to limit/control the spread of UFO cases, it's their methods that I disagree with.
So far, from the stories/rumors we hear, they only end up adding fuel to the fire and aiding hardcore believers in their false rumor campaigns. ie. "why is the government trying to cover-up UFO cases by threatening people into silence- they are behind it or know something"
This is the typical claim of hardcore believers/UFO cults.

The government should instead expose the lies of those who create hoaxes and simply mark real/unknown cases as "unkown"
Or a second alternative would be to play along with the hardcore believers and their false rumors to show the world their stupidity. "Yes we're hiding UFOs buried under the ground dig and you'll see....ohh it looks like it turned out to be a World War Two plane...so sorry we assumed it to be a spacecraft" (:P)

But hiding something humans know the existence of is only bound to increase their curiosity. That's human nature.