Unless you actually see one you aren't going to believe.
My family and neighbors saw one. Period. That's why I "know" we are being visited.
There's no point in arguing that "space is so spacious" or "it would take the energy of a star".
I was UFO curious but not a believer. My experience and that of my neighbors and family pushed me over.
I was not content to even rely on the fact that others in my family were witnesses to the event.
I talked to neighbors to see if they saw what we saw. Those who were awake at 11:00 pm saw the same things. Unfortunately, local eyewitness accounts don't carry much persuasive weight.
Crop circles? There are explanations that involve hoaxers.
Anal probes and abductions are events recovered under hypnosis.
Mutilated cattle? Why not. People do crazy things. Let's get drunk and cut up some cows and freak everyone out.
Japanese Candle Lanterns? These have caused a lot of false alarms.
I absolutely don't believe the area 51 stories. That myth is enjoyed by the wonky engineers that like to cozy up to ladies in Las Vegas and talk about their "important job" working with UFO's at area 51.
So you can see - it's easy to discount most of this stuff. But, I don't know how to discount what I (and family + neighbors) experienced.