Don't get distracted by the term "soft" as these books can be harsh and cruel indeed. For example, The Road by Cormac McCarthy could easily fit into this genre because the story focuses on the thoughts and feelings of the father with practically no detail explaining why the earth was destroyed and its food stocks decimated. However, the story is horrifying and down-right disturbing (so much so that I cannot force myself to finish it).
Included within this genre are the space opera (think Star Wars, especially episodes I-III) and science fantasy (Startling Stories, Weird Tales and other collections of pulp shorts). I might return to these later but suffice to say that soft science fiction and her sub-genres are the reason why science fiction and fantasy sit side by side in book stores.
Finally, soft science fiction is not necessarily bad science or vice versa, although some would have you believe that. Think of the hard-soft binary as a line. On the left side you have hard science based on modern, real hard sciences. On the left side you have soft sciences focusing on human relationships and problems. All science fiction exists between these two poles. If you go all one way you either end up with a scientific treatise lacking in plot or in a romance novel.*
*Please note, the romance I am describing is a literary form which engages the fantastic and the supernatural. Shakespeare's The Tempest is a romantic play which certainly lacks any modern notions of romance between the supposed lovers.