Beauty is not solely in the eye of the beholder
Beauty refers to the aesthetic appeal of something or someone. The essence of beauty is expressed through form or appearance exhibiting unity through harmony, proportionality, or some other arrangement of qualities that make it excellent. Beauty manifests itself by sparking awe, wonder, or delight in the observer. Beauty has an objective and subjective side: without a beautiful object, the subject could not be awed by beauty; without a subject to be awed, beauty would go unrecognized.
Moral relativism asserts that all good things are simply relative to the interpreter—what is good to me is not necessarily good to you (thus entailing the false judgment “we should not judge”). The phrase, “beauty is in the eye of the beholder,” represents aesthetic relativism because it asserts that the appreciation of the goodness of beauty relies exclusively upon the observer. The false assumption is that unity, qualities, and excellence are not objectively (essentially) present in anything, and so the subject imposes them on the object. The proof adduced to support this assumption is how some people applaud the beauty of some piece of art, while others are repulsed by the same piece.
The falseness of the phrase, “beauty is in the eye of the beholder,” may be discovered by looking at natural beauty. Human art serves a certain utility; it is intended to achieve some human intention. For example, art may be intended as a social statement, may function as entertainment, may constitute an intellectual exercise or expression of imagination, etc. In other words, human art has subjective goals that are not essentially connected to beauty. In fact, beauty is rarely discussed by modern artists or art critics because it is not considered part of human art production.
Natural beauty, however, does not exist to serve a utilitarian purpose for human society. Think of the Rocky Mountains. It is commonplace that a person confronted with their beauty will utter an emotional response (“Oh wow” or “That’s awesome”). We would be surprised by a person who had no emotional response to the beauty of the Rockies, suspecting they were defective in some emotional sense. The Rockies are a cause of human emotional responses of awe, wonder, or delight. They are not the sole cause because the active capacity (i.e., the efficient cause) for appreciating beauty is a human one; but, the Rockies themselves hold a certain unity of form and quality that stimulates the human response. The implication is that the Rockies are objectively beautiful, regardless of any particular failure of human affections.
If beauty is not an arbitrary and subjective declaration by a “beholder,” then the human capacity to perceive the goodness of beauty is such that we can presume there is a beautiful universe that this human capacity is formed to recognize. If so, the perception of beauty—as aesthetic appreciation, affectively generated and cognitively developed—becomes a moral virtue by which the human mind (psyche) achieves part of its excellence. Ecological ethics is birthed from the experience of beauty.