How do we know that these behaviors do not depend on agreement?
One can imagine a world in which it is acceptable to murder the weak.

Of course one can imagine such a world. No need to imagine it. There are such worlds. So what? The question is not whether this is always practiced, but whether it is always right. That is a value-question, not a factual one.
And as for your question how we know — you could ask, in general, how we know that any value is correct. There is moral intuition (conscience), and it instructs us as to what is moral and what is not moral. That is why it is so easy to confuse it with feelings of revulsion and disgust.

So is the value that says we must not harm another person, whether by action or by omission, and which is intuitively understood, the only one that stands beyond time and place, or are there other such values?

I am speaking, of course, only about moral values that do not depend on agreement, not values of another kind.

On the other hand, we can plainly see that killing fetuses and stealing copyright have become socially accepted, so even in non-aesthetic morality, the influence of society and the spirit of the times is powerful and blinds moral perception.
Therefore, in my opinion, there is really no such thing as “aesthetic morality” at all. Rather, there are basic foundations that everyone recognizes, and there are finer moral details that require sensitivity of soul and swimming against the social current in order to recognize them.
Both these and those are truth, and not merely pleasantness.

David,
With regard to moral values, it seems to me that these are only values that concern harming another person. The rest are aesthetic values. There are also halakhic values that are not necessarily connected to morality.

Roni,
The fact that the spirit of society also influences us regarding non-aesthetic values is true (see Nazi Germany, abortions, and so on), but that does not mean that this is always the case.

Okay, if what is meant by the term “aesthetic values” is to say that sometimes aesthetic feelings blind our vision and create the illusion of an objective value — just as social fashions, or desires and urges, also blind moral identification and cause a person to think that what is pleasant, beautiful, and convenient is also what is objectively good and upright — then fine, I accept that. That is presumably true. But of course, one who believes in those values is not aware of the blindness. For example, if I understand correctly, you think that opposition to polyamory stems from an aesthetic feeling and has no value beyond that, whereas I think it is a genuine value, unrelated to an aesthetic bias, but rather to a true recognition of exclusive and devoted couplehood as an ideal.

Of course. My intention was not to convince anyone of the conclusion, but to present the possibility that each person should examine for himself: whether, in his opinion, this is a value judgment or an aesthetic feeling.