There are many biblical reasons for not accepting the idea of intelligent life beyond earth other than angels and demons.
First of all, it would be impossible for morally responsible humanoids anywhere in the universe to keep from sin. If they had the genuine right of choice, it must inevitably have been used to disobey God. Thus they would require salvation.
Secondly, Jesus Christ is the only Savior, and His death is the one and only perfect sacrifice for sins ever offered in the universe (Hb 9:23-28;10:12-14). If there are morally free agents on other planets, they would have to believe in Christ for salvation.
Thirdly, God has gone to great lengths to give us an historically verifiable record of His Son's death and resurrection at the hands of eyewitnesses and this message is contained in a Bible which can be verified in many ways by the inhabitants of earth (geographically, archaeologically, etc.) and which would not be available to ETIs. It would seem both unfair and a violation of God's way of dealing with mankind for beings elsewhere in space to be required to believe in a Savior who was crucified on a distant planet.
Fourthly, the Bible seems to indicate that this earth is the only such place in the universe. When Satan is cast out of heaven, he comes to earth; it is on this planet that the battle will be fought resulting in Satan's defeat and imprisonment in the abyss; it is on this earth that Christ will reign for 1,000 years while Satan is locked up; it is to this planet that Satan will return when he is released; and it is on this planet that Satan will meet his final defeat and his eternal doom will be sealed. Finally, if life happened by chance on this earth and evolved upward, then it could seemingly happen elsewhere in the universe. But if, as we believe, human life resulted from a purposeful act of God, and if sin is inevitable for such beings, and if the human soul is the prize for which Satan and God do battle, then it hardly makes sense to have this same process repeated on countless other planets throughout the cosmos.