Heterosexism

Heterosexism is the discrimination, bias, and negative attitudes towards all non-heterosexuals on the basis of heterosexual supremacy and heteronormativity. It is based on the belief that heterosexuality and male-female monogamous relationships are the only natural and normal form of sexual expression. This system of beliefs classifies LGBTQ+ or MOGAI individuals as second-class citizens and seeks to treat them as such in society in terms of legal and civil rights, economic opportunities, and social equality. Heterosexism is harmful to all sexual orientation minorities due to how it systematically seeks to put down all people who are not heterosexual as less-than with less freedom within a society while also seeking to segregate them from society.

Heterosexism compared to homophobia is a broader term. Homophobia denotes unreasonable fear or antipathy of homosexuals and homosexuality. Heterosexism on the other hand refers to any reasoning for discriminating against non-heterosexuals including antipathy and fear as well as ignorance and selfishness as well as a bias for heterosexuality. Homophobia is also a personal opinion while heterosexism can be described as a system of self-enforced beliefs.

Heterosexism is often misunderstood to mean a distaste for heterosexuals, possibly being described as heterophobia.

History
The word heterosexism was first used by Craig Rodwell in 1971.

Etymology
Hetero is derived from the Greek word ἕτερος, pronounced héteros meaning 'other' or 'another' and is usually used in science as a prefix meaning different, referring to attraction to dissimilar genders. -ism is a suffix meaning to take the side of, to imitate, or to believe in.

Resources
Ism | Definition of Ism by Merriam-Webster