The difficulty with recovered materials evidence is that it quite possibly would contain biological contamination in the form of microbes, or perhaps even extraterrestrial DNA ( if extraterrestrial life makes use of DNA ). Think of the isolation precautions NASA used on the astronauts when they returned from the Moon. Extraterrestrial microbes would encounter an entire planet of life composed of what the infectious disease people call “ immunologically naive “ organisms. The risk would be two - way, however. H.G. Well’s “ War of the Worlds “ illustrated this.What would an alien life form have to gain, if communication were possible, by holding a press conference? Do we feel compelled to communicate with an ant mound when we discover one? If the mound is not in our yard or does not pose a threat we tend to let it go undisturbed. So it is.
I do think we have some alien materials, though anything biological seems less certain. Alleged landing and/or crash sites tend to draw the military/government rather quickly. Many are at military installations themselves, which begs the question -- if false, what would be the incentive to fabricate such incidents?
My guess is that we don't have the means to re-engineer anything. By coincidence the collection of "alien material" was discussed on Tucker Carlson just last night. And from what was reported on that program, military sightings are on the rise. This makes sense, since the military is charged with surveillance, and our capabilities have improved.
There is really no incentive for government to tell the public about any of this. I think in part because it just raises more questions than it answers. Governments like societal order and military superiority, whether communist or "free." Order and superiority are better served by keeping a lid on this and not sharing anything that might be learned. That is why the first two videos are baffling to me. It makes me wonder if there has been a change in policy, and if so, why?
Because we aren’t seeing evidence of extraterrestrial biological contamination, many people discount the idea that we are being visited, and it’s not an unreasonable assumption. It might be possible that the visitors would recognize this and somehow prevent themselves from contaminating our planet while protecting themselves from Earth’s microbes in the process, but this again makes visitation more improbable.
The only way I can see getting around this problem would be if the visitors were actually from Earth, but a different time than ours or something like a parallel universe. Pretty long odds.