What is the biblical/logical basis for rejecting the "physical" interpretation of Christ's being the Only Begotten Son? Is there any verse in the Bible or a logical construction disproving the "physical" position on Christ's being the Only Begotten Son?

I had a conversation with a Mormon and he told me that Lucifer was a brother of Christ. When I referred him to these verses:


  In this was manifested the love of God toward us, because that God
  sent his only begotten Son into the world, that we might live through
  him (1 John 4:9, KJV)
  
  For God so loved the world, that he gave his only begotten Son, that
  whosoever believes in him should not perish, but have everlasting life
  (John 3:16, NKJV)


he said that when the Bible says that Christ is the Only Begotten Son, it must be understood in terms of His physical birth, however both Lucifer and Christ had been born of God spiritually even prior to Christ's physical birth.
Christ is God's begotten son, which to relate it to human terms means he was born of God.

Lucifer, on the other hand, is a fallen angel who was created by God as were the other angels, just as man was.


  Colossians 1:15-17 NIV
  15 The Son is the image of the invisible God, the firstborn over all
  creation. 16 For in him all things were created: things in heaven and
  on earth, visible and invisible, whether thrones or powers or rulers
  or authorities; all things have been created through him and for him.
  17 He is before all things, and in him all things hold together.


These verses tell us that Christ was the firstborn, and all things were created through him.  This includes all things in heaven such as the angels.