You know that it is wrong to murder, lie, steal, commit adultery, yet you break these commandments. Thus, you know what is wrong. You have an innate sense that these things are objective, not merely your subjective opinion or feelings yet you still do them. You see the principles included and stated in most societal laws throughout history.
You're conflating moral instinct and our personal agreement with "objective morality".
You can read it that way. What I am doing is expressing a biblical truth. How you take it is up to you. That truth is expressed in Romans 1 and 2.
For those who do not have the Law and Ten Commandments revealed to them by Scripture, they show that they know it anyway by what they do and what they believe.
Take Romans 2 for example, here is the context,
14 For when Gentiles who do not have the Law do instinctively the things of the Law, these, not having the Law, are a law to themselves, 15 in that they show the work of the Law written in their hearts, their conscience bearing witness and their thoughts alternately accusing or else defending them, 16 on the day when, according to my gospel, God will judge the secrets of men through Christ Jesus.
I will supply you with the greater context,
5 But because of your stubbornness and unrepentant heart you are storing up wrath for yourself in the day of wrath and revelation of the righteous judgment of God, 6 who will render to each person according to his deeds: 7 to those who by perseverance in doing good seek for glory and honor and immortality, eternal life; 8 but to those who are selfishly ambitious and do not obey the truth, but obey unrighteousness, wrath and indignation. 9 There will be tribulation and distress for every soul of man who does evil, of the Jew first and also of the Greek, 10 but glory and honor and peace to everyone who does good, to the Jew first and also to the Greek. 11 For there is no partiality with God.
12 For all who have sinned without the Law will also perish without the Law, and all who have sinned under the Law will be judged by the Law; 13 for it is not the hearers of the Law who are just before God, but the doers of the Law will be justified. 14 For when Gentiles who do not have the Law do instinctively the things of the Law, these, not having the Law, are a law to themselves, 15 in that they show the work of the Law written in their hearts, their conscience bearing witness and their thoughts alternately accusing or else defending them, 16 on the day when, according to my gospel, God will judge the secrets of men through Christ Jesus.
The mistake I find most people make is believing that if there is a God that their own "righteousness" or "good works" will outweigh their bad or evil acts. Since God is just He must address all sin or else His justice and holiness and purity are compromised. Yet God has offered us another alternative which is not our good works but the works of Another. By faith in those, we find reconciliation with God. Jesus expressed it in John,
Jesus answered and said to them, “This is the work of God, that you believe in Him whom He has sent.”
Ephesians 2:8-10 (NASB)
8 For by grace you have been saved through faith; and that not of yourselves, it is the gift of God; 9 not as a result of works, so that no one may boast. 10 For we are His workmanship, created in Christ Jesus for good works, which God prepared beforehand so that we would walk in them.
By God's grace, when we believe by faith in the works of Another, and trust in those works to meet our righteousness, just like in OT times Israel relied on the sacrifice without blemish of animals to cover their sins, the sacrifice is acceptable to God. Notice it is not our own sacrifice that makes us right with God in finding salvation, but in the sacrifice He provides. Throughout the OT they relied on the sacrifices they brought before God to meet and atone for their sinful actions, yet God, just like with Abraham, provided the sacrifice. Instead of Abraham offering his own son God provided the sacrifice. Jesus is the sacrifice that meets God's standards of righteousness. Will you recognize that sacrifice as sufficient for your sins or not is between you and God.
In and of yourself you are a dead man towards God. What can a dead man do? Nothing. He needs resurrecting. Jesus said He is the resurrection and the life. Are you willing to trust this or go your own way? That is between you and God.
But I ask, what can a dead man do?
Ephesians 2 (NASB)
Made Alive in Christ
2 And you were dead in your trespasses and sins, 2 in which you formerly walked according to the course of this world, according to the prince of the power of the air, of the spirit that is now working in the sons of disobedience. 3 Among them we too all formerly lived in the lusts of our flesh, indulging the desires of the flesh and of the mind, and were by nature children of wrath, even as the rest.
What can a dead man do? It requires the grace and mercy of God found through faith in Jesus Christ to resurrect you. The requirement is faith, but not blind faith, reasonable faith and evidential faith.
You're also building a flimsy bridge from "don't murder" (OK) and "don't lie" (OK) with "don't covet" (not morally wrong) and "don't worship false gods" (not morally wrong) and "don't dishonor your parents" (not morally wrong).
You're lumping all of these together as if they were all equally "objective" while only making a case for 2 out of the 10.
Each one of these things is against loving your neighbour or God. Each one of these things leads to all kinds of other crimes or sinful actions. Love is looking out for others above yourself, of putting their interests first, above your own. It protects and hopes goodness on others. It does not mistreat them. It looks out for their best interests.
How you treat others reflects on how you treat God since Genesis discloses humanity is created in His image and likeness.
Objective morality must be a set of clear, non-context-sensitive, Quantifiable LOGICALLY COHERENT principles and or specific rules that each have specific, prescribed consequences that have NO EXCEPTIONS.
All you've provided are SUBJECTIVE guidelines (no death penalty for cursing a parent) with zero detectable consequences (eternal hellfire + whatever your local government says).
The death penalty was a Mosaic law. Prove otherwise? The principle is that it is good to honour your parents who brought you into the world and looked after you for all those years, however imperfectly.
Do you recognize there is a difference between the two covenants or not? Do you see what laws are expressed in both? Do you see the same penalty for disobeying the Ten Commandments in both Testaments?
The guidelines are not my own. They are found in the Bible. Whether you want to believe they are objective truths and principles is up to you. Try explaining morality otherwise.
I am well aware of the ditty that goes, "Convince a man against his will he remains the same unchanged still."
That is where your volition or will plays in the whole thing. Is what I say reasonable to you? Do you see the need for an ultimate objective, fixed measure for morality or is relativism okay with you? If not, make sense of morality for me and it will be my turn to question you.
Now, if you see the need for a fixed standard then what is the necessary standard to make sense of morality?
Once you answer "god," which God? What is God like? That is an entirely different conversation.
