No alien that we know of has ever come to Earth.
As far as not seeing aliens, some aliens are microbes. Probably most are microbes. It’s hard to see microbes without a microscope.
It already is being used for military purposes right now as in spy satellites. Even very recently SpaceX was tasked to launch a U.S.but it exploded and the satellite didn’t make it.
In 1984 arocket launched the and satellites for “reconnaissance,” and the satellite for missile detection. The list just starts there and goes into the hundreds including many satellites and so on.
And, by the way, not just by the United States, but other governments as well.
Furthermore, the Chinese government once shot a missile to destroy their own satellite in space just to say the could, and they succeeded, vastly increasing the dangerous debris cloud floating now in orbit. It was a military demonstration.
There is no stigma. All of science is dedicated to discover extraterrestrial life. We would be completely excited to find even a fossil of a microbe from space because it would be the ultimate affirmation that life can evolve from matter on another world other than Earth. Our best hope at present is to find some kind of life on one of the moons of Jupiter or Saturn, or perhaps some fossils on Mars as of yet undiscovered. We are even spending billions of dollars with the SETI program to listen for radio waves from space!
However, much to the surprise and dismay of scientists, we have yet to discover anything at all.
Mechanical, intentional interstellar travel is unlikely since the distances are far too great to imagine. The best anyone could achieve is interplanetary travel within one’s own solar system. Therefore, if we pass the buck and say life didn’t start here but started somewhere else and arrived here, it would have had to arrive on a rock or asteroid as a microbe and somehow survive a fiery entry through Earth’s atmosphere and it would have had to survive the vacuum and temperature extremes of space. If the rock came from outside the solar system it would have had to survive a long, long time.
After awhile, walking on the moon got old. It cost a whole lot of money and there wasn’t much to do there. The Vietnam war was sucking the budget. We were sending men up there to kick around the dust and rocks, drive rovers around, and it – as I said – cost a lot. Can you give me a good reason to go back?
No. Andy Weir’s “The Martian” was science fiction. It was a possibility, but not a reality at present. Don’t confuse science fiction with reality.
We shouldn’t go to Mars (in my opinion) but we are going anyway. That being said, we have to wait and see how it plays out in reality, not in sci-fi.