We know there is a lot of life that exists in conditions that are very different from humans. Just some of their environments include extreme heat/cold, heavy pressure, darkness, in water, under ground. And we know that life comes in many different sizes (as big as a house or microscopic). We also know that many animals are far stronger than humans. We know that animals have other abilities for vision, smell, hearing, and communication that we can't sense or understand. And we know that other creatures have social aspects (ants, bees, lions, monkeys, etc.).

Combine all of that with the vast universe. Expand what we consider the Goldilocks zone to account for the different types of life, and there could be many alien species out there. And we could just be an interesting science study for them if they were here. I've always found science fiction such as The Day the Earth Stood Still to be somewhat plausible. We are making fast advancements in technology but we are also still very disconnected and prone to war and destruction. If I was studying a species with our characteristics and history I would be both fascinated and concerned.