There are those of a religious bent who believe that the Bible is clear about there not being sentient life anywhere else in the universe.
The Bible states that Jesus died once for our sins. But if that is the case then Jesus couldn't have been born, lived, preached, and been crucified on multiple worlds. But if Jesus didn't appear on other worlds then it would be cruel for God to create those sentient beings and give them absolutely no clue as to the One Way to salvation.
So these folks tend to believe that if there are UFOs that are not weather phenomena or military exercises then they must be demons.
It will be interesting if there are aliens and they do make themselves known to us. Most people will treat them as other beings that we either can work with or have to fight against. At the same time there will be a huge number of traditional religious folks who will believe them to be demons and act accordingly. Could be very chaotic.
How do people ‘act’ against demons?
Another inquisition of those they consider in league with them?