This contradicts the ethicist’s reasoning, which is that the “beauty” argument is less open to logical objections and directly addresses what makes nature worth preserving.

The ethicist never claims that nature’s moral value—or any other characteristic—is an insufficient reason to preserve nature.

The ethicist says that it’s philosophically disputable whether nature has moral value, but never says that nature would be more worth preserving if it didn’t have moral value.

The ethicist isn’t concerned with whether or not nature has moral value—or even whether it’s actually worth preserving. The argument is just about which argument in favor of preserving nature is less vulnerable.

The ethicist says that beauty is a basis for preserving nature, which is indisputably beautiful, and uses that to conclude that beauty is a less vulnerable basis to argue for preserving nature. This principle articulates the unspoken assumption to which the argument conforms.