You are really making it a habit of misrepresenting scripture by removing verses/passages from their context and causing them to be generalized. Whether its malicious or not, you are also missing important details within certain verses as well as ignoring some key things about my position that I have made very clear...
1. Deu 21:18-21 contains both laws that a son is breaking, and a penalty (capital punishment in this case) for breaking laws. Like I've stated many times, the messiah's body paid for the earthly penalties (curses) associated with breaking "old" covenant laws.
The only punishment for the parents and men of the city is if they do not follow the law:
"If thou wilt not observe to do all the words of this law that are written in this book, that thou mayest fear this glorious and fearful name, The Lord Thy God; Then the Lord will make thy plagues wonderful, and the plagues of thy seed, even great plagues, and of long continuance, and sore sicknesses, and of long continuance. Moreover he will bring upon thee all the diseases of Egypt, which thou wast afraid of; and they shall cleave unto thee. Also every sickness, and every plague, which is not written in the book of this law, them will the Lord bring upon thee, until thou be destroyed." - Deuteronomy 28:58-61 KJV
There are examples of implemented laws that allowed capital punishment for disobedient sons and daughters that come from Deut 21: https://en.wikipedia.org/wiki/Stubborn_Children_Law
Christ fulfilling the law wasn't about "doing the jail-time" or covering the "cost of the punishment" so much as covering the requirements of the law in our stead.
2. I'm not saying that this is what you were inferring, but just in case you were.... this is not speaking of young children. Unruly... yes. And someone's son... yes. But this is speaking of a "bitter, worthless, alcoholic"... not a young kid.
3. This is one out of context situation in an entire court system... A parent couldn't just decide that his son (not young child) was being unruly and just go stone him. Just like how we have for capital punishments in our society today, there were many other things in place before it could get to that point:
"If a man have a stubborn and rebellious son, which will not obey the voice of his father, or the voice of his mother, and that, when they have chastened him, will not hearken unto them: Then shall his father and his mother lay hold on him, and bring him out unto the elders of his city, and unto the gate of his place; And they shall say unto the elders of his city, This our son is stubborn and rebellious, he will not obey our voice; he is a glutton, and a drunkard. And all the men of his city shall stone him with stones, that he die: so shalt thou put evil away from among you; and all Israel shall hear, and fear." - Deuteronomy 21:18-21 KJV
If a parent submits their son for execution and standard of evidence is met, can a judge then say that the son is still innocent in the eyes of the law despite the evidence? Is it a requirement for the judge to honour the law and allow the child to be stoned to death?
Is it a sin against God to disobey this law and spare the child the death penalty?
But that is the law... unless you are suggesting that a priesthood, elder, or judge can adjust the law to the circumstance?
We see interesting examples in the OT of equivalencies. "An eye for an eye" A lost eye needn't be repaid with a literal eye. That lost eye may be repaid with a monetary equivalent (e.g. "free the blinded slave in exchange for the value of his eye"). The law has many examples of fulfilment through equivalency. That doesn't mean that in doing so that the law is ignored or that one becomes an apostate of the law. Hardly.
The New Testament gives the ultimate equivalency for all commands in the law: "For all the law is fulfilled in one word, even in this; Thou shalt love thy neighbour as thyself." - Galatians 5:14 KJV
1) Either the law must be completed as written, in legalistic exactitude, and parents are to submit their unruly children for execution, and kill their own children.
Or:
2) The law is fulfilled by equivalency through the new covenant. Love is the equivalent for the specific commandments in the OT. A parent may choose on their own terms (drawing from their heart) how to deal with their children.
There is an insidious nature of equivalents paid without the constraints of coming from a place of God's love shown in the NT. If these equivalents are made without the love of God in our hearts, every sin is simply atoned for by blood sacrifices or trivial activities that by man's standard that are purported as equivalents. The NT tells us that the only equivalent, the only way to truly fulfil the law, is by the love in our heart that comes from God. That love is found through Jesus Christ.
"Transferring" sin to a chicken or some other questionable blood sacrifice on the day of atonement might be a creative way from a man-made perspective to fix the gap between the law and human behaviour. Accidentally flipped the nonkosher light switch in your house on the Shabbat? Kill a chicken on the right day of the year and call it even. Bore false witness against someone you later realized was a fellow tribesman? Maybe kill a bigger animal and call it square. Grab 39 of your buddies, made a solemn oath to God not eat until a particular preacher is killed for heresy, but he skips town and you can't find him in a reasonable time? Give up, eat your fill wipe your mouth, and maybe kill an ox or two for atonement and say you've done nothing wrong. Maybe some animals that were not to be saved from danger are good for sacrifice too?
Some of these equivalents can be made in a loveless fashion. The vast majority of them are man-made and are not from scripture. We could play the games that the Pharisees played and straining gnats at the expense of camels, but the covenant of the new testament is a requirement to truly fulfil the law. Not by word for word letter of the law legalism, but as the equivalency offered through Christ's sacrifice and the inward essence of God's love that is required to grow in order to partake in that covenant.
It would be like a landlord stating that so much money must be paid each month for a lease term, but you present him with 10 bars of gold upfront instead and the landlord finds the alternative arrangement agreeable.
If Christ's sacrifice only covered the penalties of sin, why do women still have periods and painful labour? Clearly this isn't the Christian concept, the Christian concept is that Christ covers the requirements of the law, not the penalty by itself.