How can anything be established as good or bad? We, collectively, agree that certain things are good and certain things are bad. But how do we come to establish and derive the morals that we possess currently? For example, let's imagine a hypothetical society where rape culture is encouraged. If even a majority of the members of this society were to agree that rape was acceptable (even those who are subjected to rape despite their discomfort because of societal pressure), then rape, in this society, would be considered an act of virtue or an act that is neutral to moral analysis. It would be, in this society, unreasonable to question the act of rape as immoral. In fact, in today's society, many people agree that it is acceptable to kill animals for the sake of our consumption (even if it discomforts them). It is agreed, in certain cultures, that this is moral. However, how could we ever possibly conclude whether this is moral or not? Animals certainly wouldn't like being killed.
So, long-story-short, how could we consider something moral? Must a majority of society agree? Should those that are elder than us determine what is moral? How could we objectivity define an act as moral?