I'm sure some people could argue that to have enemies inspires a person to higher goals, but that would be based on selfishness and it is a road to a dead end for the group and victory for the individual, as we see in current day society getting worse and worse. Instead if we were more Ubuntuism as a species, where nobody wins unless everybody wins, that would lead to a faster advancement of the whole of the species and a more even spread of resources. This would benefit everyone, make everyone feel more a part of the process, and create a smooth flow of forward progress.
Humans seem to have a psychological need to have enemies. Is it ethically necessary to have enemies? Probably not in everyday social situations. Opposition and struggle can be helpful for growth. I don't know that I would use the word "enemies" though.