Christians would not do that, because Jesus did not disregard the Hebrew Scriptures.
But it is important to recognize that the Law Covenant that was given through Moses, was given to the Israelites. So these words must also be acknowledged:
12 Jehovah said further to Moses: 13 “Speak to the Israelites and tell them, ‘Especially, you are to keep my sabbaths, for it is a sign between me and you during your generations in order that you may know that I, Jehovah, am sanctifying you. 14 You must keep the Sabbath, for it is something holy to you. Whoever profanes it must be put to death. If anyone does any work on it, then that person must be cut off from among his people. 15 Six days work may be done, but on the seventh day is a sabbath of complete rest. It is something holy to Jehovah. Anyone doing work on the Sabbath day must be put to death. 16 The Israelites must keep the Sabbath; they must observe the Sabbath during all their generations. It is a lasting covenant. 17 It is an enduring sign between me and the people of Israel, for in six days Jehovah made the heavens and the earth and on the seventh day he rested and refreshed himself.’”
Psalm 147:19, 20
19 He declares his word to Jacob,
His regulations and judgments to Israel.
20 He has not done so with any other nation;
They know nothing about his judgments.
So God did not provide this Mosaic Law to all nations, but all nations will be blessed through the children of Israel who kept the Law. However, this Law was also designed to provide the laws and order for a nation. Sometimes the Israelites obey the Law, and are blessed, and sometimes they do not, and God authorizes that they be punished according to the Law.
When God said that this or that law is punishable by death, this told the Israelites that God will judge them and other humans by their obedience to those laws.
Sometimes God would forgive truly repentant people for a transgression that would have incurred death, like what happened to David when he took another man's wife and arranged for that man to be killed - two commandments broken, and some very bad things happened to David's family and the nation because of it.
On the other hand, when he saw that a transgressor's heart is rebellious, God can punish such a person immediately himself, like when the man who knew God's sabbath law decided to publicly pick up wood right after God told Israel to keep that law. Or, when a Levite (who was obligated to know and teach the Law) named Uzzah decided to break God's law about who and how they must transport the Ark of the Covenant, by putting the ark on a precarious wagon, and then grabbing it when it jostled.
Jesus understood all of these things. He knew and exemplified with his life that the sabbath was made for man, not man for the sabbath. He knew, as the faithful prophet Samuel said to King Saul, that rebelliousness is as bad as divination, which is from the demons. 1 Samuel 15:22-23
So Jesus emphasized his God and Father's view of Law - which can be merciful when there is repentance, but it must also be taken seriously when he gives it because the wages that sin pays is death.
Jesus' sacrifice of his perfect life provides a ransom for those who want to change their lives in repentance, and who put faith in him. This makes the Law Covenant obsolete, as Paul pointed out:
13 Furthermore, though you were dead in your trespasses and in the uncircumcised state of your flesh, God made you alive together with him. He kindly forgave us all our trespasses 14 and erased the handwritten document that consisted of decrees and was in opposition to us. He has taken it out of the way by nailing it to the torture stake.*
* Greek, "stauros'"
4 For Christ is the end of the Law, so that everyone exercising faith may have righteousness.
So, this is not disregarding the Old Testament, but rather a continuation of God's purpose to bless people of all nations, not just the Israelites, for salvation.