Aliens would not physically come to Earth until they were sure of our threat level. I assume that if they had the capability to come to Earth from as far away as four light years, the distance to the nearest star to our sun, they would have technology far beyond our own. They would have more advanced radiation shielding, propulsion and spacecraft design. The assumption that they would also have more advanced weapons than anything we have, as well, would not take a big leap in logic.
The aliens would be aware of our rapid advancements through the twentieth century, through our broadcasts of radio and television. They would also be aware of our capacity for war and that we appear to be hell bent on self-destructing. Maybe they would recognize it as a phase we, as a species, are passing through. Maybe they would not; however, they would approach us with caution.
If their intent were hostile, they would have acted before now. If they were merely curious, they would maintain an observation post a safe distance from Earth. Possibly cloaked in orbit around our planet, they would study us. They wouldn’t risk an encounter, even for scientific reasons. It is unlikely that their technology would be so backward, relative to the sheer feat of coming here at all, that they would need to capture and probe anyone. They haven’t initiated first contact, so they would hardly come down to earth for any reason, given our obvious paranoia.
That we are the sole intelligent species in the universe is an unrealistic belief. Aliens are out there, but may not be interested in us until we demonstrate that we have evolved beyond the primitive need for war. So far, we have not. We have the potential to meet and trade with aliens, but we must first survive the phase of self-destruction that we face today. We hope that we are poised on the brink of that evolution, but recognize that it is not a certainty. We hear voices for peace around the globe. Nations are learning to work together to solve complex problems and while the negotiations don’t always go smoothly or produce results, the fact that they take place at all is a giant step forward.
Until we leave this self-destruct phase, aliens will not contact us. They will watch us, perhaps, but they will not come to Earth.