Isaac Asimov once said that he had no argument with reports of UFOs. "It's the IFOs that bother me," he added. Yes, there are unidentified objects seen in the sky. But the conclusion that these unidentified objects are extraterrestrial visitors is unsupported by any solid evidence, even after more than half a century.
Turn the question around. Look at the UFO phenomenon from the viewpoint of the alleged alien visitors. If you had traveled across many light-years of space and found a planet that bears intelligent life, would you confine your activities to stunt flying in the dark of night and abducting random individuals for obscure medical examinations?
More likely you would either announce your presence in an unmistakable manner or you would keep yourself hidden from human detection while you study the Earth and its inhabitants without interfering with the subject of your study.
There may be myriads of highly advanced extraterrestrial civilizations. Their representatives may indeed be swarming over our planet. We simply have no credible evidence of it.
During the American Civil War, when reports from the battlefields were often unreliable, many newspapers used a headline that warned their readers that the story they were about to read might not be accurate. The headline was, "Good News, If True."