Sarah-kate tends to binge-drink several times during the week, passing out in random places throughout her apartment. when confronted by her roommate, sarah-kate defends herself, saying that her roommate also drinks, as do most people their age. today's researchers would call this:

I believe the answer is: the false consensus effect.
the false consensus effect refers to a type of bias where people overestimate the strength of their  beliefs, opinions, or preferences.
This often caused after those people resided in an ideological buble that prevent them from being confronted by differing ideology.