Mainstream literature generally shies away from such explicit content. However, in some underground or niche publications, there might be something that could be considered in that realm, but it's not part of the mainstream. So, generally, no, you won't find true erotic swinger stories in regular mainstream literature.
One alternative theme is historical events. Many books are based on real historical periods, like the World Wars or the Renaissance. Authors use these settings to tell stories about the people who lived through those times, their struggles, and their achievements. Also, the theme of family is very prevalent. Family dynamics, whether it's a loving family or a dysfunctional one, can make for very engaging stories.
These types of stories, if widespread, can have a negative impact on society's moral values as they promote non - traditional and often inappropriate sexual behavior.
Mainstream media aims to reach a broad and diverse audience. Erotic swinger sex stories are inappropriate because they are sexually explicit and not in line with the values that mainstream media typically promotes, such as family - friendly, educational, and positive social values.
This is a complex matter. On one hand, in a consensual and adult - only context, some might argue that as long as all parties involved are fully aware and agreeing, it could be seen as a form of adult sexual exploration within the boundaries of legality. However, from a more traditional or conservative moral perspective, it goes against the norms of monogamous relationships and family values. So, it really depends on different ethical frameworks.