Monosexism. This is the result of power structures in society that give more validity to being attracted to only one gender. These structures deter or even punish anything that doesn’t obey this norm. Usually, it’s bi+ people who suffer because of this. People feed monosexism when their attitudes back this norm, even in subtle ways. Institutions of society can uphold monosexism, and messages society sends are part of it too. For example, these messages imply it’s impossible to feel attraction to more than one gender over the course of your life, or they convey prejudice against bi+ people.

Synonyms:
monosexist, monosexists