Soft Science Fiction

No such thing! Soft SciFi is an undefined term that does not fit into the lattice of genre assessment.

But since some people are painfully slow in realizing that Science Fiction is more related to the Fantasy genre than any scientific publication, the term might be thrown around to describe the opposite of Hard science fiction when what is really meant is any Science Fiction without the restrictions of 'hard' science. If one were to brave the impossible challenge to devise a comprehensive overview of genres in fiction, Hard SciFi would be a subcategory of Science Fiction, not it's opposite.