This is what the Gospel Principles manual says about Outer Darkness:
These are they who had testimonies of Jesus through the Holy Ghost and knew the power of the Lord but allowed Satan to overcome them. They denied the truth and defied the power of the Lord. There is no forgiveness for them, for they denied the Holy Spirit after having received it. They will not have a kingdom of glory. They will live in eternal darkness, torment, and misery with Satan and his angels forever. (See D&C 76:28–35, 44–48.)
Note there is no mention of needing to see God or Jesus. Or to have a perfect knowledge.
I'm not necessarily agreeing with your opponent here, but the problem here is that you've not looked at all the doctrine on the subject. For example:
D&C 76:31 . To What Extent Must a Person Know God’s Power and Be a Partaker Before He Becomes a Son of Perdition?
To become a son of perdition one must sin against the Holy Ghost, but before that is possible, one must receive the gift of the Holy Ghost. Elder Melvin J. Ballard explained that “unto the Holy Ghost has been given the right and the privilege of manifesting the truth unto men as no other power will. So that when he makes a man see and know a thing he knows it better than he shall ever know anything else; and to sin against that knowledge is to sin against the greatest light there is, and consequently commit the greatest sin there is.” ( Millennial Star, 11 Aug. 1932, pp. 499–500.)
Elder Joseph Fielding Smith further explained why sin against the Holy Ghost is so serious: “The Spirit of God speaking to the spirit of man has power to impart truth with greater effect and understanding than the truth can be imparted by personal contact even with heavenly beings. Through the Holy Ghost the truth is woven into the very fibre and sinews of the body so that it cannot be forgotten.” (“The Sin against the Holy Ghost,” Instructor, Oct. 1935, p. 431.)
The Prophet Joseph Smith asked, concerning those who become sons of perdition, “What must a man do to commit the unpardonable sin? He must receive the Holy Ghost, have the heavens opened unto him, and know God, and then sin against Him. After a man has sinned against the Holy Ghost, there is no repentance for him. He has got to say that the sun does not shine while he sees it; he has got to deny Jesus Christ when the heavens have been opened unto him, and to deny the plan of salvation with his eyes open to the truth of it; and from that time he begins to be an enemy. This is the case with many apostates of the Church of Jesus Christ of Latter-day Saints.” ( Teachings, p. 358.)
Elder Spencer W. Kimball wrote: “The sin against the Holy Ghost requires such knowledge that it is manifestly impossible for the rank and file to commit such a sin” ( Miracle of Forgiveness, p. 123).
Of apostates who had committed the unpardonable sin, the Prophet Joseph Smith said: “When a man begins to be an enemy to this work, he hunts me, he seeks to kill me, and never ceases to thirst for my blood. He gets the spirit of the devil—the same spirit that they had who crucified the Lord of Life—the same spirit that sins against the Holy Ghost.” ( Teachings, p. 358.)
People do not come to such a state in a moment. Elder Joseph Fielding Smith described the path that some follow, which would cause them to hate God and his servants: “The change of heart does not come all at once, but is due to transgression in some form, which continues to lurk in the soul without repentance, until the Holy Ghost withdraws, and then that man is left to spiritual darkness. Sin begets sin, the darkness grows until the love of truth turns to hatred and the love of God is overcome by the wicked desire to destroy all that is just and true. In this way Christ is put to open shame, and blasphemy exalted.” ( Instructor, Oct. 1935, p. 432.)
Such people have placed themselves outside the redemptive powers of Christ (see Hebrews 6:4–9 ; 10:26–29 ; Matthew 12:31–32 ). They cannot partake of His mercy because they cannot incline themselves to repent, having totally lost the Spirit of God. Their sin “is an offense so heinous that the sinner is unable to repent; and this is what makes his case hopeless. If he could repent, he could be forgiven; but being incapable of repentance, he cannot be reached by the pardoning power.” (Orson F. Whitney, Improvement Era, Mar. 1920, p. 413.)
“In the realms of perdition or the kingdom of darkness, where there is no light, Satan and the unembodied spirits of the pre-existence shall dwell together with those of mortality who retrogress to the level of perdition. These have lost the power of regeneration. They have sunk so low as to have lost the inclinations and ability to repent.” (Kimball, Miracle of Forgiveness, p. 125.)
Doctrine and Covenants Institute Student Manual
Section 76 - The Vision of the Degrees of Glory
Do I see attitudes displayed here sufficient for Outer Darkness? Yes, I believe I do. Do I think that all apostates who die in that state will inherit OD? No, I don't.