Is Paul's morality obsolete today?

Today, I skip one chapter and will return to chapter 4 tomorrow. I would like to deal with some ethical issues.
Paul heard that a Christian in Corinth was known to live with his father's wife. Paul was very strict and unforgiving to some sinners and demanded the church in Corinth to remove them from the community. This one was no exception because Paul considered the sin so bad that even pagans did not practise.
Let him who has done this be removed from among you (1 Corinthians 5:2b).
Why did Paul not tolerate such sins? It was understandable because Paul was a Pharisee. These Pharisees were famous for keeping the letters of the law so sincerely that sometimes, they failed to appreciate the real-life situation of the others. Moreover, the image of leaven leavening the whole lump cut deeply into his mind.
Do you not know that a little leaven leavens the whole lump? (1 Corinthians 5:6b)
This unaccommodating attitude towards sinners is self-defeating. Sooner or later, the church would rid herself of nearly all members. Only a handful of elites would be able to remain in the church. The church would not be a church of sinners. All the members would be saints without sins. They would not need God anymore! Soon, they would drive God out of their church. That's why it is self-defeating to drive sinners (and God) out of the church.
The image of leaven leavening the whole lump is misleading. The leaven is active while the flour lump is passive. But such is not an accurate description of the interactions taking place in the church. The church is not a passive flour lump. She is made up of many members. It is true that sinners would exert bad influence on members who faith is weak. This is what the leaven image conveys. Yet, there are members who faith is stronger. They will be able to call up their potential to counteract the bad influences. The presence of sinners in the church "forces" Christians to practise forgiveness and charity. Moreover, let us forget not that the Holy Spirit is abiding in the Church, sanctifying her. Driving out sinners indicates a lack of faith in people and in the Holy Spirit. Therefore, the theology expounded in chapter 5 is rather problematic. It is strongly Pharisaic in smell.
Matthew was a tax-collector. He was more sympathetic with sinners. What is more, he himself had experienced the accommodation of Jesus when Jesus was willing to dine with them. Therefore, the way he dealt with public sinners of the church was more accommodating as well.
and if he refuses to listen even to the church, let him be to you as a Gentile and a tax collector (Matthew 18:17b).
Furthermore, it is Matthew who reported Jesus' instruction to forgive 70 times 7 (Matthew 18:22). In the gospels, tax-collectors and Pharisees are natural enemies. Their treatments of sinners couldn't be more diametrically opposite!
Paul knew the Torah very much. Most of the time, he would translate the text into Greek directly and did not copy from the Septuagint. However, the quotation in the last verse of chapter 5 is very much identical with the Septuagint text. One wonders if this comes from the hands of Paul or from some scribe secretary.
ἐξάρατε τὸν πονηρὸν ἐξ ὑμῶν αὐτῶν.
Drive out the wicked person from among you. (1 Corinthians 5:13)
καὶ ἀφανιεῖς τὸν πονηρὸν ἐξ ὑμῶν αὐτῶν.
So you shall purge the evil from the midst of you. (Deut 13:6, LXX; Deut 13:5 MT)

My dear Advocate, I pray for the One, Holy, Catholic, Apostolic Church. You are the guarantee of our eternal life. May You protect the Church from evil leaven within. May we sing praises to You day by day. Amen.