Objective morality is an oxymoron. The reason this is the case, is moral codes try to control irrational impulses, for the good of the team. However, irrational impulses are not always easily reached or controlled with reason.
For example, we have laws against drugs. Since these drug taboos are more contemporary; 1920's, the laws were instituted by secular, instead of religious means. How is that working out? The drug problem has expanded since the first secular taboo. The logic behind not doing drugs, may be sound, but it does not reach the irrational impulses of the people who routinely ignore the law.
Truth is better than lying, in any rational system, since truth allows for clarity and good data is best for drawing the best curve. So why do politicians lie to the masses? We have separation church and state, so this objective morality is based on secular rules, that claim to be rational, yet they are ignored.
When you deal with the irrational side of humans, sometimes an irrational system works better. If we had God having a tempter tantrum if you do X, this irrationality can reach the irrational side of the violators. It may not be as effective for the rational person, who does not see the logic. However, law was not made for the righteous, but for the irrationally impulsive; sinners.
Say I do something that is irrationally impulsive, thereby harming the team; immoral behavior. If I can rationalize it, after the fact, and make myself appear to the victim, is that objective morality?
Defense lawyers do this in court. Defense lawyers will try to appeal to not only logic but also to the emotions of the jury, to help justify the irrational behavior of their client. They need some irrationality within the jury to help some members of the jury, justify the bad behavior, or in some cases, reward stupid behavior.
There was a case in the USA where a woman was rewarded $millions for burning herself with hot coffee, she had just bought from a fast food restaurant. She put aside her reason and got a reward for a blond moment, from an irrationally induced jury. We need another way that can deal with all the irrationality, both within criminals and juries.
Does anyone remember the Russian Collusion Coup where the Democrats led Swamp tried to railroad an innocent man? How many in this forum, who call themselves rational, fell for the coup? The reason you bore false witness, was you were manipulated into irrationality, and allowed yourself to put aside your reason. There was too much fun, beating on an innocent man, who was framed. Your rational code was place on the back burner. Objective morality is not always good enough for the irrational side of humans, which is the main source of all types of violations.
The religious Right, who uses the morality of God, as the litmus test, were able to suspend their irrationality easier, so they got this right. Thou shall not bear false witness, requires you have all the facts before jumping on the band wagon of herd irrationality. Secular morality pushed by the Left does not require that; an immoral code.