Carver's "Neighbors" is a story about voyeurism: the natural, human tendency to want to live the lives of others and see how others live. The story doesn't suggest this is positive or negative, it just is, and a one-line cliche certainly can't explain a Raymond Carver story.
The story doesn't make value judgments. Given the opportunity to investigate the lives of their neighbors, the husband and wife, but particularly the husband, since the "camera on the wall" point of view follows only him, is aroused, sexually and otherwise. The idea is that, given the chance to do the same, in privacy, we are all like the husband and wife in the story. The story simply presents a kicked-up version of looking into someone else's medicine cabinet.
In short, the story does reveal elements of human character--we are all voyeurs, to an extent. Remember, the couple appears to be completely normal until they get into the neighbor's apartment. The story suggests that they are still being normal, even inside.
"Neighbors" can be seen as an argument about human character because of the freedom the Millers suddenly acquire to explore the Stones’ apartment once the Stones leave. An old saying has it that "Character is what you are and what you do when you are totally alone." Once Bill and Arlene are alone and unwatched (each one is separated from the other when exploring the apartment of the Stones), their curiosity transforms them into peeping Toms and even burglars. The story raises the issue of the nature of human character, but does not provide answers about the issue, for the locked door puts a stop to anything even weirder than the Millers have already done. (But irrationality and uncivilized behavior seem to be their basic characteristic.)