To believe that we humans are the only intelligence in this vast universe is just too much to fathom. To believe other intelligent beings have visited us (in our tiny part of this vast universe) is also too much to fathom. We are just not that important when you look at the big picture.
The universe is too big for just us to be here.
I kinda think that aliens are like an advanced version of humans. Cave people had smaller brain cavities and more musculal bodies, needed to survive back then.
Aliens, at least as they are portrayed, have smaller less muscular bodies with a very large brain cavity, owing to the increase brain size and assumeably increased intellect and less reliance on physical strength.
So, I wonder, are the alien civilization potentially advanced humans in the future?
Well, maybe some by natural selection get stamped out...