Answer

It is logically impossible to ground values in facts. That is the naturalistic fallacy. But facts can cause a person to understand what is morally right and wrong. The way to discuss values is through rhetoric, not logic. You can’t do it by means of a well-constructed logical argument, but rather by pointing to various consequences, understanding the situations, and that can sometimes lead a person to realize they were mistaken and change their values. The fact is that this does happen quite often. Of course, this is not a guaranteed method, and it will not always end in agreement. But that is true of any discussion, not only discussions about values.