I don't accept your premise here. There clearly is a "we"
We don't live in a vacuum, many things I do on a day to day basis affect other people, and the things they do affect me. The interaction between individuals is where the "we" comes from.
Out it this way, if morality exists, in any way you want to define it, it is at the very least concerned with how actions may affect other people.
Morality quite obviously exists - whatever you want to define it as - because we have a word for it and I think most people understand and agree what the concept is, even if we don't accept where morals come from.
You don't appear to be arguing for where morals come from. You seem to be arguing that morals don't exist at all. And without wanting to straw man you, if that is your position then I think you are wrong, and quite clearly wrong.
Okay, meta-ethics, it is.
This can be answered using basic science.
Can it be observed that humans make choices based on values? Yes.
Can these values be observed to be independent of human cognition and feelings/emotions? No!
There are no objective moral values in the same sense as gravity is common to all humans.
You have 2 categories:
Takes place independent of human cognition and feelings/emotions; i.e. e.g. gravity.
Takes place dependent on human feelings/emotions and sometimes influenced by cognition; i.e. e.g. whether it is wrong to kill another human.
Now because we can share cognition and feelings/emotions, 2 or more humans can share the same moral values, but that doesn't make it independent of human cognition and feelings/emotions.
As to interaction, if someone helps someone else, that is a "we". If someone hurts someone else, that is a "we", right?!!
There is no "we" independent of shared values, trading, voluntary cooperation or forced cooperation.
Now morality and ethics are several categories:
The moral value assigned to a behavior.
The set of moral values a person holds.
The idea that we should include others in moral consideration.
The attempt with reason, logic, evidence and/or faith to make a system of how to arrive correct moral answers.
I need water, if I don't get that, I die, but you don't die, if I don't get water. There is no "we" in biology, evolution takes place at the level of the duplication/replication of genes. Some species form some form of cooperation, but that doesn't mean that there is an uniform species, which survives at the level of the species.
Humans are a social species; i.e. individuals, which rely on groups. But there is no overall group in the human species.
Now to arrive at a universal "we" requires, that you believe in that. That you hold a set of values, which include all humans. There are other sets of values out there. Just look at the world and you will see them.
So back to another post:
Lawrence Kohlberg:
Stage 6. Universal Principles. People at this stage have developed their own set of moral guidelines which may or may not fit the law. The principles apply to everyone.
E.g., human rights, justice, and equality. The person will be prepared to act to defend these principles even if it means going against the rest of society in the process and having to pay the consequences of disapproval and or imprisonment. Kohlberg doubted few people reached this stage.
https://www.simplypsychology.org/simplypsychology.org-Kohlberg.pdf
Morality as universal is not born into humans. It is learned and is connected to cognition as it requires the combination of reason, logic, evidence and feelings/emotions.
But it still doesn't make it universal/common as e.g. gravity. It just means that a given person holds a set of universal values. Note that it is practice properly not possible, but rather stage 6 is an ideal to shoot for.
Further for the 10 to 15% of humans, who can do this in principle, because of the required cognition, they don't share an exact set. The individual sets only overlap to a certain degree.
So here is an example of such a set of principles. Note they are not rules, they are guiding principles.
https://www.uua.org/beliefs/what-we-believe/principles
Notice in the link: What we
believe!!!
Regards