the deliberate or ongoing process of excluding particular groups of people from something; the opposite of incorporating inclusion.
The institution of marriage was, and still is in many respects and countries, Queer exclusionary: that is, by restricting marriage to opposite-sex couples, Queer people were excluded. Other institutions, such as religious institutions (e.g. churches) also excluded Queer-identified people, deeming them unworthy of participation.
Sadly, there are some groups within the Queer community that are exclusionary; for example, some gay and lesbian groups may be bi-exclusionary, by deeming bisexual+ people as not being “gay enough” to participate; and the increasing rise in trans exclusionary spaces and groups that act in opposition to trans-identified people.