So a flying saucer crashed at Roswell (or perhaps lots of saucers in lots of places), the US Government recovered the wreckage, and has 'reverse engineered' the saucers to create their own saucers, and magical sources of 'free' energy which could create energy independence for the US, etc. And much of modern technology was actually developed by reverse engineering crash debris, and we actually have the ability to 'take ET home' (i.e., travel among the stars). Or so the story goes...
The notion that much of modern technology is reverse engineered from ET technology is absurd to anyone familiar with the history of science and technology. Where are the huge discontinuities in progress that such a claim implies? And why would anyone make these claims? While it may simply be an entertaining story, perhaps intended to earn money for the storytellers, a disinformation operation, or a honeypot intended for foreign intelligence services, perhaps a better explanation is that it conveys the message that UFO secrecy and the heroic efforts of the USG to sustain it have brought the US great benefits; and the ET technology and capabilities aren't really that mysterious or advanced, and shouldn't really frighten anyone; and we should trust the government's policy, and support the continuing secrecy. At the worst, this argument might have been used to badger USG officials into supporting the UFO 'cover-up'. Clearly such an argument, at least in the present day, is not intended for those familiar with the behavior of UFOs and the history of human technology.
It's certainly understandable that the military would regard the possibility of creating their own flying saucers, etc., based at least partly on reverse engineering ET technology, as of supreme importance to the national security of the US. And the possibility that the Soviets (or now, the Russians or Chinese, etc.) might have similar debris, and might use it to create weapons systems far superior to USG's would have been a nightmare to the US military. Perhaps these concerns would have been enough to justify, for at least some National Security officials, over 60 years of psychological operations conducted against the American people to suppress not only the details of the alleged crash(es) and engineering efforts, but even the reality of UFOs and the ET presence.
Perhaps the US has learned a bit about materials, energy, etc., and perhaps even has primitive 'anti-gravity' systems. Attempts to understand the relationship between electromagnetism (et al.) and gravity, e.g., predate the modern UFO era, as do various designs involving circular or rotating electromagnetic devices claimed to have gravitic effects. But has the US created anything with capabilities approaching those of UFOs?
There are several problems with the idea of reverse engineering ET technology.
The first problem is that the human race couldn't natively reverse engineer so much as a toilet on a starship--not for a billion or even a trillion dollars. Perhaps for a billion dollars, the military industrial complex could create a genuine 'reverse-engineered UFO toilet seat', and sit on it, and declare success, and make some money for taxpayers by putting it in an amusement park and charging visitors to sit on it. But the human race does not have the scientific knowledge, and not in the wildest dreams of any rational person do we have the native engineering capabilities to design, build, test, or operate a system with anything close to the capabilities of flying saucers.
A simple thought experiment, for those familiar with the performance characteristics of flying saucers, might help to understand this better...
A fully loaded F-22 accidentally flies through a time warp and crashes in the New Mexico desert in 1947. Can the US reverse engineer the technology and change the course of history?
The military officials (in 1947) can see that it's a jet airplane, with missiles, rockets, and bombs--and a really nice gun!--and the labels are in English. But the performance and weapons are obviously far superior to the F-80, etc. Now consider the thousands of parts, millions of design decisions, all the supporting technologies (communications, maintenance systems, refueling tankers, GPS, etc.), all the science--aerodynamics of supersonic flight, materials science, electronics, etc.--and all the manufacturing infrastructure and other requirements. How long will it take the US (or any other nation) to create these?
Without the cybernetics, humans can't design, build, or test an F-22. Even worse, humans don't (directly) fly F-22s--the cybernetics does. And the cybernetics of an F-22 and supporting systems simply could not be created, even if they could be understood, in 1947--or even in 1977. By 1997 scientists and engineers might have begun to understand, and perhaps even recreate the cybernetics...but so what? By 1997, the actual F-22 (in our 'timeline') was already under development. Perhaps the military will have learned a few things in six decades from studying the crashed F-22, but the F-22 is a child's toy compared to a flying saucer, and there is exactly no possibility we have natively reverse-engineered the complex systems of a far post-'Singularity' civilization.
Secondly, why did the saucer crash at Roswell? Is it even a real flying saucer? Why did the ETs permit us to have these materials? They know that humans, including the Americans, are violent and irrational, and the US military is and likely will be extremely hostile to the ET presence. Unless the ETs are incompetent or complete idiots, they would not have permitted the US to have materials which might allow us to develop capabilities which seriously threaten their activities here or elsewhere. And, as their interaction with our nuclear weapons shows, they aren't idiots, and they aren't incompetent, and they will not permit anything resembling the current human race to develop any threat which they cannot manage.
They may also know something which the National Security element of the USG doesn't seem to know, or perhaps even care about: that if we continue on our current path, we won't survive long enough to create anything useful from the crash debris. In other words, civilizations which reach our level of technological development--without a proportionate understanding of consciousness, spirituality, and the nature of our existence--will almost inevitably fail...and that at this point, only an experience as wrenching as contact could cause us to change our course of development.
And even if the US could achieve aerospace supremacy with respect to other nations, times have changed, and there are many critical threats other than Soviet bombers of 1947 (and a few years later, nuclear armed missiles)--for example, biological and cybernetic threats, either of which could be fatal to the United States. And thus even the extreme possibility--absolute aerospace supremacy, etc.--while a huge strategic advantage, can no longer ensure our survival.
Moreover, if we survive the next few years, humankind will eventually acknowledge the ET presence. Even if the US will have meanwhile created wondrous new energy technologies, imagining that the US and its corporations will become enormously wealthy at the expense of other nations, does anyone imagine that other nations will tolerate this without demanding the ETs provide them with equal or better technology?
If the ETs simply plan to eat the human race on Thanksgiving Day 2012, or have some other malevolent purpose, then they won't care what the human race does, as long as we don't exterminate ourselves, spoiling their dinner plans.
But if they have the slightest interest in the possibility of a constructive long-term relationship, then they won't begin it by contributing to the wealth and power of one nation at the expense of all the others, and thus infuriating most of the human race.
In perhaps the worst case, the US would have used reverse engineered technology to kill people in other nations in one or more of our wars. The ET presence becomes known someday, and the people of the other nations are outraged, demanding not only compensatory, but punitive damages, and the ETs feel obliged to comply, to the great detriment of the US. Even if the USG was foolish enough to make this mistake, the ETs, unless they're idiots or don't care about a possible future relationship with humankind, wouldn't allow such a situation to develop in the first place.
Finally, there is no 'free energy' and never will be. There are better technologies for producing energy than are commonly used today, and such technologies will certainly have significant economic impacts--on the petroleum industry, e.g. But in our society, governments will regulate and tax any new energy source, and global corporations, e.g., the major oil companies ('energy' companies), will continue to make large profits through investments, acquisitions, and political influence.
Obviously there are many reasons why the USG might want to continue the UFO/ET secrecy. But if, however improbably, the possibility of reverse engineering recovered ET technology is still one of those reasons, does the intelligence and analysis really support this argument?