I'd tell him you're absolutely correct. Your lifestyle IS NOT a sin. Lifestyles aren't sinful. Lives are. And my life is just as sinful as his. But if you're committing homosexual acts, in accordance with God's word, that is sin.
But we've all got a sinful lifestyle and we've all made a practice of sinning in it. They have chosen to deal with their brokenness through repeating the same sin.
Do you lust? Do you covet? Do you tell white lies? Do you cheat at anything?
If you consistently did these things, would you term your lifestyle as sinful too?
No, you are missing the point entirely. Of course I have done some of those things, but I was convicted and repented and asked God to help me not to do them. That is the difference. These people don''t see what they do as a sin. So they don't think they need to repent. And, yes, it most certainly is a practicing lifestyle.
1 John 3:8-10 (NASB)
8 the one who practices sin is of the devil; for the devil has sinned from the beginning. The Son of God appeared for this purpose, to destroy the works of the devil.
9 No one who is born of God practices sin, because His seed abides in him; and he cannot sin, because he is born of God.
10 By this the children of God and the children of the devil are obvious: anyone who does not practice righteousness is not of God, nor the one who does not love his brother.
"Whosoever is born of God does not practice sin!"
Why? Because he has a new nature within him, and that new nature cannot sin. John calls this new nature God's "seed."
So don't put true Christians in the same state as lost sinners, because they are not. Yes, all sin, but some practice this lifestyle of sin with no repentence or remorse. If they can do this and get by with it, then I am doubtful they are saved, no matter what the sin.
Hebrews 12:5-11 (GenevaBible)
5 And ye have forgotten the consolation, which speaketh unto you as unto children, My son, despise not the chastening of the Lord, neither faint when thou art rebuked of him.
6 For whom the Lord loveth, he chasteneth: and he scourgeth every son that he receiveth.
7 If ye endure chastening, God offered himself unto you as unto sons: for what son is it whom the father chasteneth not?
8 If therefore ye be without correction, whereof all are partakers, then are ye bastards, and not sons.
9 Moreover we have had the fathers of our bodies which corrected us, and we gave them reverence: should we not much rather be in subjection unto the father of spirits, that we might live?
10 For they verily for a few days chastened us after their own pleasure, but he chastened us for our profit, that we might be partakers of his holiness.
11 Now no chastising for the present seemeth to be joyous, but grievous: but afterward, it bringeth the quiet fruit of righteousness, unto them which are thereby exercised.
When a person receives Christ as his Saviour, tremendous spiritual changes take place in him. He is given a new standing before God, being accepted as righteous in God's sight. This new standing is called "justification." It never changes and is never lost.
The new Christian is also given a new position: he is set apart for God's own purposes to live for His glory. This new position is called "sanctification," and it has a way of changing from day to day. On some days we are much closer to Christ and obey Him much more readily.
Bible Exposition Commentary - Bible Exposition Commentary – Be Real (1 John).