For if the
many many died by the trespass of the one man how much more did God’s grace and the gift that came by the grace of the one man, Jesus Christ, overflow to the many!
16 Nor can the gift of God be compared with the result of one man’s sin:
The judgment followed one sin and brought condemnation, but the gift followed many trespasses and brought justification.
17 For if,
by the trespass of the one man, death reigned through that one man, how much more will those who receive God’s abundant provision of grace and of the gift of righteousness reign in life through the one man, Jesus Christ!
18 Consequently,
just as one trespass resulted in condemnation for all people, so also one righteous act resulted in justification and life for all people.
19 For just as
through the disobedience of the one man the many were made sinners, so also through the obedience of the one man the many will be made righteous. (Romans 5:13-19) (emphasis added)
Yes, we do act in accordance with our nature and these verses make clear that we are all condemned by Adam's sin. We all fell when Adam fell. The entire human race. We all became equally guilty before God. We all inherit a sinful nature. Read on in Romans where Paul writes about this battle between the "old man" and the "new man" and the bondage of the flesh to sin. You say this makes God responsible for our sin?
10 Not only that, but Rebekah’s children were conceived at the same time by our father Isaac.
11 Yet, before the twins were born or had done anything good or bad—in order that God’s purpose in election might stand:
12 not by works but by him who calls—she was told, “The older will serve the younger.”[
d]
13 Just as it is written: “Jacob I loved, but Esau I hated.”[
e]
14 What then shall we say? Is God unjust? Not at all!
15 For he says to Moses,
“I will have mercy on whom I have mercy, and I will have compassion on whom I have compassion.”[
f]
16 It does not, therefore, depend on human desire or effort, but on God’s mercy.
17 For Scripture says to Pharaoh: “I raised you up for this very purpose, that I might display my power in you and that my name might be proclaimed in all the earth.”[
g]
18 Therefore God has mercy on whom he wants to have mercy, and he hardens whom he wants to harden.
19 One of you will say to me:
“Then why does God still blame us? For who is able to resist his will?” 20 But who are you, a human being, to talk back to God? “Shall what is formed say to the one who formed it, ‘Why did you make me like this?’”[
h]
21 Does not the potter have the right to make out of the same lump of clay some pottery for special purposes and some for common use?
22 What if God, although choosing to show his wrath and make his power known, bore with great patience the objects of his wrath—prepared for destruction?
23 What if he did this to make the riches of his glory known to the objects of his mercy, whom he prepared in advance for glory—
24 even us, whom he also called, not only from the Jews but also from the Gentiles? (Romans 9:10-24) (emphasis added)
Romans 9:19-20 responds to your accusation. We, as a race, chose to sin. Do you think any of us would have succeeded where Adam failed? Adam had the ideal situation (and Eve). They were surrounded by nothing but goodness and there was no sin but when they encountered sin (through Satan) they wanted sin more than obedience. The very first time they were tempted they sinned. Do you want to blame God for that too? Why did God create them with a nature that could choose to sin? Why did God allow Satan to come and tempt them? If God had just created all of us with a perfect nature incapable of sin then there would be no need for hell for anyone. Same with the angels. There would be no demons or hell if God had not created the angels with the ability to sin. God took the sin nature out of the angels who remained faithful just as in heaven we will no longer be capable of sin.
Is God unjust in allowing us to sin and then judging us for it? The answer is Romans 9:23. You say we do not have a sin nature so why do we sin? Yes, we are made in the image of God but not in His precise image as God cannot sin. Only Jesus was made in the precise spiritual nature of God as He is God. We sin because it is our nature to sin. Only through faith in Christ can we receive a new nature that has the ability to resist sin. This is the "new man" Paul writes about.
I bow to the sovereignty of God. I do not think God unjust. He has every right to do with his "clay" what He wishes. God is pure holiness. We might not always understand His ways but it is clear from Scripture that all men born of a mother and a father receive a sin nature due to the disobedience of Adam. God in His mercy provided a "second Adam" to save us - Jesus Christ. God did not have to provide a "second Adam." He could have justly left us in our sins and punished us. A sin nature is not a human invention.