Person A using the couch for its intended function (a place to sleep over) vs B who is using it also for social function with possible slight degradation in faculties (drunk), lowering of social barrier (socializing).

What you say is true: it is cool and positive social experience on travels are fantastic. However, objectively, A has a lower risk profile. B is creating doors to possible negative outcomes. These doors may never open for B, but for A’s risk profile, some of these doors (paths to potential negative outcomes) do not even exist.

Additionally, for the potential predator, A’s behavior raises risk for the predator and B’s lowers it. So B type behavior raises possibility of negative outcome at both levels: vulnerability is raised for victim, and control over the situation and outcome (i.e. assault) is increased for the predator.