If you believe in the Religion of Naturalism and millions of years, you must conclude aliens exist. That is, the walking, talking, reasoning, Klingon kind. 

If you don’t believe in millions of years, you must conclude aliens do not exist.

If you believe in Biblical Authority, earth is God’s special creation, where man was created, where man sinned and broke relationship with God, where Jesus came to restore man to God, and the salvation of Jesus is not extensible to ET.

If you don’t believe in Biblical Authority, you believe God could have created life elsewhere, and the need for alien life to be saved is laughable.  This creates doubts in the need to be saved for man on earth.