I would like to talk about my experience with science. I am mentally disabled.
To me, sociology and psychology and psychiatry should be integrated. Instead, these three sciences are separated into three boxes. I was once in a room with a psychologist who dismissed the effect of society's perceptions of people on the mentally ill and disabled. How society views people does have an effect. When a person who has no friends reads in a popular magazine that people who don't have friends is a loser, this has an effect on the person. Loners are treated in movies as either savants or violent sociopaths of psychopaths. Try getting a job or loans without friends or references. In most cases, it won't happen. Psychiatrists tell a mentally disabled person to go to a therapy group, and their job is to give medication to people. Psychiatrists treat medicine like candy - have a problem, take a pill. The pill isn't working, increase the dosage. Psychologists attempt to help people with mental illness by assigning causes to the illness from a person's history. The person is isolated from context and studied. It's like attempting to glean a history of an object by putting it in an empty room and doing tests on that object. Archaeologists would be against this, because the context is lost. Context is where the object was found and what was found with the object. For humans, context is the environment and the society we live in. The result is that people who are mentally disabled like me are given treatment that doesn't address fully the disability, because we are treated with less respect and less care than a common everyday vase.
I don't know if aliens visited our world in the past. Most of our history has been lost through various causes. And, sometimes, people don't understand what they are looking at. For instance, I was reading about a piece of thread that was found in Canada. Scientists weren't sure what they had, and placed it in a box in a museum and forgot about it. A decade ago, another scientist who was familiar with the sewing methodology of the Vikings identified the thread as being a relic of their civilization. Her investigations would lead to the discovery that the local Dorset culture was trading with the Vikings.
I personally believe that aliens have visited our system, either directly or indirectly, and have determined that contacting us is not in their interest. We have nothing of value to trade, and we are not at their technological level. The aliens may even have their own version of the Prime Directive.
I doubt very seriously that our world will ever be invaded. One of the benefits of us finding other worlds is that we realize how little value our world has in the broader scale. There are an unknown number of worlds, and an alien civilization would rather take resources from a world that is not populated by an intelligent species that can fight back.