Notice it does not say that "if we say that we do no sin, we deceive ourselves, and the truth is not in us."
If it said that, it would be in contradiction to 1 John 3:5-9, in the immediate context of the epistle.
It says, "If we say that we have no sin, we deceive ourselves, and the truth is not in us".
It is speaking of indwelling sin as an element within us.
This element can be crucified, rendered dead (Romans 6:6, Galatians 5:24, Romans 7:8) so that it no longer has any say over our behaviour (Romans 6:14). We are in no way obligated to obey the flesh (Romans 8:12 (kjv, NLT)).
This means that it is not biblical that sin, as a practice in our lives, is inevitable.
Maybe you have a general idea of what sin is, but you seem to be under the impression that people can obtain a state of sinless perfection. People sin often and regularly even when they don't realize it.
Even Paul admitted he is not perfect:
Philippians 3:12
12Not as though I had already attained, either were already perfect: but I follow after, if that I may apprehend that for which also I am apprehended of Christ Jesus.
The only way Paul's confession of not being perfect makes sense is if he continues to sin occasionally. Romans 7:14-25 confirms what Paul said in Philippians 3:12, which is that he's a human who is susceptible to the same struggles as the rest of us and occasionally fails.
While it is a biblical statement to say that we will continue to have the element of sin dwelling on the inside of us for the rest of our lives.
However it can be crucified, rendered dead (Romans 6:6, Galatians 5:24, Romans 7:8).
Except in Philippians 3:12, Paul admits he isn't perfect. So your definition of crucifying the flesh and/or rendering the flesh dead isn't compatible with Paul's stated lifestyle. That most likely means your interpretation isn't correct or there wouldn't be any contradictions in your narrative.
Crucifying the flesh isn't something that just happens. Having received a new born again Spirit we now have a spirit that seeks to so God's good pleasure, but it's a choice.
Philippians 2:13
13For it is God which worketh in you both to will and to do of
his good pleasure.
1 Corinthians 9:27
27But I keep under my body, and bring
it into subjection: lest that by any means, when I have preached to others, I myself should be a castaway.
Except that Paul made it clear that he became as weak in order to win the weak; which indicates that in the whole of what he wrote as scripture, he was not lying.
Fundamentally, any form of manipulation is a kind of deception and that's like lying.
I'm aware of what Paul said in 1 Cor. 9:19-23, but he didn't use literary tactics to fool people into thinking he can be a trusted member of their incrowd in order to persuade them to accept the gospel of Christ. If that's the case then he used manipulation and lying.
When Paul spoke of his struggles with sin in Romans 7:14-25, the only way it makes sense is if he was being bluntly honest about his real and tangible struggles.
Holy means "holy". Do you understand that the word "holy" does not only mean to be "set apart" but that it means to be "set apart from sin"?
Absolutely, but Christians are holy, not because they never sin, but rather because of Jesus.
Romans 3:21-24
21But now the righteousness of God without the law is manifested, being witnessed by the law and the prophets;
22Even the righteousness of God
which is by faith of Jesus Christ unto all and upon all them that believe: for there is no difference:
23For all have sinned, and come short of the glory of God;
24Being justified freely by his grace through the redemption that is in Christ Jesus:
Too many people fall for the teaching today that holy does not mean holy. This is something that was prophesied in 2 Timothy 4:3, btw. Also, in Jude 1:3-4.
Holy does mean holy, but I think you believe holiness is works-based. It isn't.