Maybe not, maybe there is an infinity of variation of objective morality. There will always be broken people with pathologies like sociopathy or narcissism that wouldn't agree. But the vast majority, like 95% of people would agree for example on the universal human rights - at least if they had the rights and freedoms to express themselves and the education to understand and not be brainwashed. Basically given the options of a variety of moralities and the right circumstances (safety/not in danger, modicum of prosperity, education) you would get an overwhelming consensus on a large basis of human rights or "truths". The argument would be that just because a complex machine is forever running badly, that there still can be an inherent objective ideal of how it should run, even if perfection isn't desirable or the machine and ideal has to be constantly improved.
There is another way to argue for a moral starting point: A civilization that is on the way to annihilate itself is "doing something wrong" - because any ideology or morality that argues for annihilation (even if that is not the intention, but the likely outcome) is at the very least nonsensical since it destroys meaning itself. You cannot argue for the elimination of meaning without using meaning itself, and after the fact it would have shown that your arguments were meaningless. So any ideology or philosophy that "accidentally" leads to extermination is nonsensical at least to a degree. There would still be an infinity of possible configurations for a civilization that "works" in that sense, but at least you can exclude another infinity of nonsense.
"Who watches the watchers" is of course the big practical problem because any system so far has always been corrupted over time - objectively perverted from the original setup and intended outcome. But that does not mean that it cannot be solved or at least improved. A basic problem is that those who desire power/money above all else and prioritize and focus solely on the maximization of those two are statistically most likely to achieve it. That is adapted or natural sociopathy. We do not really have much words or thoughts about this and completely ignore it in our systems. But you could design government systems that rely on pure random sampling of the population (a "randocracy"). This could eliminate many of the political selection filtering and biases and manipulation. But there seems very little discussion on how to improve our democracies.
Another rather hypothetical argument could come from scientific observation of other intelligent (alien) civilizations. Just like certain physical phenomena like stars, planets, organic life are naturally emergent from physical laws, philosophical and moral laws could naturally emerge from intelligent life (e.g. curiosity, education, rules to allow stability and advancement). Unfortunately it would take a million years for any scientific studies on that to conclude.
It is quite possible that it's too late now, or practically impossible to advance our social progress because of the current overwhelming forces at work in our civilization.
Having objectivity in our system doesn't mean our morals are based on objective things.
Is it objectively wrong to kill?
You can't answer that with a "yes" or "no", because it depends so much on the subjective situation.
Also, arguments which you say "like, uh, 95% of people", by guessing kinda devalue your whole comment. You dot need to not write what you were thinking, but instead say something like "they may not be completely objective, but our subjective views are so similar that practically we do have objective morality in certain contexts".
Which would be true.
The "95% of people believe in basic human rights" isn't. Utterly naive.
I'm not arguing for "one single 100% objective morality". I'm arguing for social progress - maybe towards one of an infinite number of meaningful, functioning moralities that are objectively better than what we have now. Like optimizing or approximating a function that we know has no precise solution.
And "objective" can't mean some kind of ground truth by e.g. a divine creator. But you can have objective statistical measurements for example about happiness or suffering, or have an objective determination if something is likely to lead to extinction or not.
There will always be broken people with pathologies like sociopathy or narcissism that wouldn’t agree [...]
And dismissing their way of perceiving the world is a choice which we make, not an objective mandate or imperative. We do it because the benefits to us ("normal people") seem to outweight the loses.
[...] at least if they had the rights and freedoms to express themselves and the education to understand and not be brainwashed
And how do you determine who falls in this category? Again, by a set of parameters which we've chosen.
[...] nonsensical since it destroys meaning itself [...]
Which is a judgement call you've externalized, again not an objective reality. You have chosen to believe that meaning is important, that self-destruction is bad. There's nothing in the universe that inherently holds this as being true. Whether one person or one billion people choose to believe something as true has no bearing on whether or not it is actually true.
You cannot argue for the elimination of meaning without using meaning itself, and after the fact it would have shown that your arguments were meaningless
You needn't argue for the elimination of meaning, because meaning isn't a substance present in reality - it's a value we ascribe to things and thoughts.
And how do you determine who falls in this category? Again, by a set of parameters which we’ve chosen.
Sure, that is my argument, that we choose to make social progress based on our nature and scientific understanding. I never claimed some 100% objective morality, I'm arguing that even though that does not exist, we can make progress. Basically I'm arguing against postmodernism / materialism.
For example: If we can scientifically / objectively show that some people are born in the wrong body and it's not some mental illness, and this causes suffering that we can alleviate, then moral arguments against this become invalid. Or like the gif says "can it".
I'm not arguing that some objective ground truth exists but that the majority of healthy human beings have certain values IF they are not tainted that if reinforced gravitate towards some sort of social progress.
You needn’t argue for the elimination of meaning, because meaning isn’t a substance present in reality - it’s a value we ascribe to things and thoughts.
Does mathematics exist? Is money real? Is love real?
If nobody is left to think about them, they do not exist. If nobody is left to think about an argument, it becomes meaningless or "nonsense".