Professional photographers take their images in RAW format to preserve all of the available information in the scene. We then develop the photographs to bring out such qualities as proper white balance, color tones, exposure, etc. Amateur photographers generally take their images in jpeg format, allowing the camera to make the development decisions.
If a professional photographer, in developing an image, makes the daytime sky green, everyone knows it has been altered beyond reality. If a photographer makes a Milky Way photograph with the foreground full of light and the Milky Way spectacular in a dark sky, the viewer might not know that this is also altered beyond reality. Most commonly, Milky Way photographs are a combination of two separately exposed photographs.
As long as the photographer lets the viewer know what has been done to the photograph, I see no issue. But if two photographs are combined to make an image, the photographer has an ethical responsibility to let the viewer know.
The Milky Way
The Milky Way is observed at its brightest and prettiest when there is no light from either the moon or human activity. But this darkness means that there will be no light on any foreground object such as a mountain range or a forest. Only a black silhouette against the stars is possible. No matter how bright the stars, they will not light the scene in a Milky Way exposure. I want my photographs to reflect this reality and have a foreground in black silhouette.
The nighttime Earth sky has color. “Airglow” is nighttime sky color caused by cosmic rays (high-energy radiation originating outside the solar system) colliding with molecules in the atmosphere. Oxygen collisions create a yellow-green color between altitudes of 53 to 60 miles, and then create a reddish color up to 200 miles. Nitrogen collisions create purple, magenta, and blue. Even in a completely dark sky, these colors are difficult to see with the unaided eye. But they are revealed in photographs using the Milky Way exposure of 10-30 seconds.
The Full Moonlit Landscape
The full moonlit-landscape is softer and more richly colored than the sunlit-landscape. But this visual wonder is somewhat wasted on us, as human eyes have evolved to function best in daylight. We can enjoy the night with our eyes, but it takes a long exposure on a camera to bring out the totality of the visual splendor of the night.