Paul is talking about something else.
And yet you cannot give an example of that something else when it was listed inbetween the sexual sins of fornication & lasciviousness which is sexual excessiveness, when all three sexual sins were following the sexual sin of adultery. Eventually it wen t beyond that category of sexual sins, but you would be remiss to categorize uncleanness as not a sexual sin that masturbation can be seen as identified as.
The word in this verse is ἀκαθαρσία (akatharsia) which is a defilement in either a physical or moral sense.
Although fornication is mentioned below, the same applies to adultery, uncleanness & lasciviousness for comitting sin against your own body.
1 Corinthians 6: 18 Flee fornication. Every sin that a man doeth is without the body; but he that committeth fornication sinneth against his own body. 19 What? know ye not that your body is the temple of the Holy Ghost which is in you, which ye have of God, and ye are not your own? 20 For ye are bought with a price: therefore glorify God in your body, and in your spirit, which are God's.
Romans 12:1 I beseech you therefore, brethren, by the mercies of God,
that ye present your bodies a living sacrifice, holy, acceptable unto God, which is your reasonable service.
So masturbation can be seen as sinning against your own body, defiling yourself in both physical & moral way when sex was created for when the two are joined as one for reproduction purposes since God commanded mankind to multiply.
This was given for those that cannot contain themselves that they find themselves at risk for burning which the temptation of masturbation can be seen as a release from, and yet, it was the burning that was to be avoided.
1 Corinthians 7:8 I say therefore to the unmarried and widows, it is good for them if they abide even as I. 9 But if they cannot contain, let them marry: for it is better to marry than to burn.
If masturbation was okay, what is the danger of burning then?
Proverbs 6:27 Can a man take
fire in his
bosom, and his clothes not be burned?
Then there is this among all the N.T. references that you so readily dismiss:
Jude 1:17 But, beloved, remember ye the words which were spoken before of the apostles of our Lord Jesus Christ; 1
8 How that they told you there should be mockers in the last time, who should walk after their own ungodly lusts....23 And others save with fear, pulling them out of the fire; hating even the garment spotted by the flesh.
I have to say that masturbation along with "coming" can certainly spot the garment with the flesh as in sperm.
I do not think the apostle would be very happy with the translators using tamay/unclean for that term.
Leviticus 15:1 And the Lord spake unto Moses and to Aaron, saying, 2 Speak unto the children of Israel, and say unto them,
When any man hath a running issue out of his flesh, because of his issue he is unclean. 3 And this shall be
his uncleanness in his issue: whether his flesh run with his issue, or his flesh be stopped from his issue, it is his uncleanness.
Paul having been a Jew, along with the remaining disciples of Jesus, would have a need to clarify what the sexual sin of uncleanness was if masturbation was okay.
They never did, and so therefore as described above, masturbation as the term used today is the term of uncleanness as used in the Bible, both O.T. & N.T..
That still leaves a HUGE hole in your presentation: to tie ἀκαθαρσία to masturbation.
1 Corinthians 2:13 Which things also we speak, not in the words which man's wisdom teacheth, but which the Holy Ghost teacheth; comparing spiritual things with spiritual. 14 But the natural man receiveth not the things of the Spirit of God: for they are foolishness unto him: neither can he know them, because they are spiritually discerned.
Sometimes the infirmity in the flesh of a saved believer having the Holy Ghost, are not open to receive edification as long as that part of him as the natural man believes what he is doing is natural and not sinful. Prayer is needed to Jesus Christ for that natural saved believer to see the truth.
John 8:30 As he spake these words, many believed on him. 31 Then said Jesus to those Jews which believed on him, If ye continue in my word, then are ye my disciples indeed; 32 And ye shall know the truth, and the truth shall make you free....36 If the Son therefore shall make you free, ye shall be free indeed.