I don't have a full answer, but a couple of thoughts.
First, Paul is writing to the whole church in Corinth, not to individuals. Is someone has gone astray, it is for the church to discern collectively how to deal with the situation.
True...unfortunately, the church I currently attend is not very...spiritually minded. The pastor has a fleshly take on everything, believes the Left's nonsense, fleshes evangelism to a ridiculous place, so on and so on. He believes that a person who calls himself a Christian can be a Liberal at the same time, and that affects his understanding of many things.
Second, Paul addresses what people do, not what they believe. For example, many people are gay-affirming, but not engaging in homosexual sex. That's probably a distinction to bear in mind.
Oh, yes...absolutely. The problem with that is, no born again person walking with God will affirm homosexuality, because (in God's own words) it is a gross abomination. That was the point of the OP...a person who supports sinful activity in any fashion, partakes of the sin that they affirm or support...
1 Corinthians 10:21
You cannot drink the cup of the Lord
and the cup of demons. You cannot partake of the table of the Lord
and the table of demons.
Ephesians 5:7*
Therefore,
do not make yourselves an accomplice to such people;
Ephesians 5:11
And
do not become a participant in the works of darkness with those who are in darkness, which produces the wickedness of bad fruit; but rather demonstrate that they are wrong;
1 Timothy 5:22
Do not be hasty in the laying on of hands,
nor take part in the sins of others; keep yourself pure.
II John 1:9-11*
Whoever does not abide in the teachings of Christ, but instead goes beyond what He has taught us,
that person does not have God. Those who do abide in His teaching, the same has both the Father and the Son.
If any one comes to you bringing another doctrine, do not receive, acknowledge, or embrace him or his doctrine into your house, do not even give him a pleasant salutation: because those who give him a pleasant salutation partake in his morally wicked and malicious works.
I think you may have overstated the Bible's opposition to homosexuality and abortion. They are both lines in the sand in western culture wars, but the Bible has far more to say about other issues such as oppression of people in poverty.
I have overstated nothing, and it does not matter if Scripture addresses "other issues" in far more abundance. A lie is a lie, and all liars will end up in the lake of fire. Homosexuality and abortion are indeed part of the modern culture wars - but the fact still stands that God trumps modern culture. If you think that God and the Bible must bend and yield to modern culture, then you are part of the problem. God's Word remains the same; homosexuality is a gross sin, as is the butchering and shedding of innocent blood. God will not step off from that pronouncement one ounce.
Last, there's the question of discernment- how might God be at work in a person's life. Are they moving closer to Jesus or persistent in rejecting his teaching? For example, my church strongly upholds traditional marriage values. A person is now beginning to attend who is living unmarried with their partner. What to do? Insist they break it off or get married right away? Bar them from services until they do? My pastor's approach is not to rush the Holy Spirit's conviction. The right time will come as they are learning the cost of following Jesus, and how to address the issue. Until then, it's welcoming them and always pointing to Jesus.
Sounds like a "seeker friendly" church...and while I agree that tactics must be applied in all situations, God will not save or bless a person living in sin. No where in Scripture do we find that a person's sin and repentance is not addressed. In that situation, the person needs to be made aware of the facts of scripture on that point, and that person must decide whether or not he is going to follow after God or his sinful lifestyle. The Scriptures cannot be watered down and be effective at the same time. As for the moving of the Spirit, He can only move upon what this person has been told...and if he has not been told that he is living in a sinful situation that God condemns, then waiting upon the Spirit to move him towards repentance and action is not a very intelligent thing to do, knowing what Scripture teaches.
God-given wisdom and discernment, not applying a hard and fast rule.
The problem here with that is this: Jesus Himself said that the whole gospel must be preached, not parts of it that won't offend people. He said that the gospel truth will offend people not really searching and seeking Him...watering down the truth only hurts that person and the person who is watering it down, because that person will be judged for doing so. We cannot lead everyone to Christ, because not everyone wants Christ. Those who do want Him, when they are confronted with what God says about their life, they will repent and take action...those who do not really want Christ will walk away. That is no big deal, because if they truly do not want Him, then they will never commit and never come to Him for salvation.
Blessings
..