1. Scripture does not mention "ET" visits.
The Bible, The revealed written Word of God, teaches that life is only possible through a process of creation. Even if there were other galaxies with planets very similar to Earth, life could only be there if the Creator had fashioned it. If God had done that, and if these beings were going to visit us one day, then He would surely have enlightened us about this.
God has given us rather specific details of he future - for example, the return of Jesus Christ, and some details about the end of the world. The universe will, at some future point, be rolled up like a scroll (Isaiah 34:4 ; Revelation 6:14). If God had created living beings elsewhere, this would automatically destroy their dwelling place as well. Adam's sin caused all of creation to be affected by the curse, so why would a race of beings, not of Adam's (sinful) seed, have their part of creation affected by the curse, and then be part of the restoration brought about by Christ, the last Adam? All of this would seem exceedingly strange.
Some have claimed that the nephilim, or the "sons of God," both mentioned in Genesis 6:2 - 4, were aliens. This is a wild extension of a common view that the "sons of God" who married the "daughters of men" were fallen angels, and that the nephilim were products of those "marriages."
"Sons of God" is clearly used of angels in Job 38:7. Here, the Septuagint translates "sons of God" as "angels of God." This need not mean that evil angels, or demons, actually cohabited with women, Jesus made it clear that angels do not engage in sexual activities, at least not angels in Heaven (Matthew 22:30). Nevertheless, evil angels on Earth could have used the bodies of ungodly men, by demonic possession, to achieve their evil purpose of producing an evil generation of people (Genesis 6:12).
To be continued...
Sign of Design: It is meaningless to claim that scriptural authority applies only to "religious things," since the Christian gospel is all about real things, the origin, history, and destiny of man and the universe. Remove its claim to authority in the realm of science, and you are actually removing it from any relevance to the real world.