I think the thinker who addressed the questions you're asking the best was Immanuel Kant. Kant believed firmly that there are universal values all rational beings will agree upon, if we think about them thoroughly enough. That doesn't mean there won't be a wide range of variation between cultures or between different time periods. But in whatever culture, in whatever time, there will be a beautifulness seen in the human form, for instance. That might vary between cultures and over time. Plump persons may be seen as "beautiful" in the art of one period while thin people are considered beautiful in another era. Or the styles of cosmetics and hair/clothing will change. But overall there is a desire for beautiful expression of the human form in the art of all cultures and times. The ancient philosopher Plato thought in ways like this too -- that there is an ideal of beauty, of truth, etc, that exists out there in the universe somehow. The attempts we make to express it are all trying to grasp that ultimate form of beauty somehow.
I think in this quote, Zeus is referring to the fire as the "evil thing in which they may take pleasure to their gut," because he refers to it right before he uses the word evil to describe it.
