When people assume that Wicca has to be heteronormative it is often because of the pairing of The Goddess/ The God. While, I will not argue that these terms can be problematic and I’m totally in favor of people making adjustments that fit them better. And perhaps, Wicca would be better off without those terms. Still, there are many reasons why Wicca does Not have to be practiced in a heteronomative way.
Here are just some things to think about as far as heterosexism , Wicca and the God/Goddess combo:
1: The Goddess and God are not just lovers. The Goddess and God are portrayed as Mother and Son. There are also myths of two Gods. Such as the Gods who highlight the dark and light halves of the year. The God and Goddess are not just some literal heterosexual couple.
2: Symbolism: Both the God, Goddess and their relationship often symbolize aspects of nature, seasons, human existence, spiritual journey, etc. Wiccans who have overly focus on there being some power in an hetero-union are sadly missing all the symbolism.Over focus on literalism is often an avenue to oppressive religious ideals
3: The Goddess represents everything including all gender, sexual and nonbinary expressions. The Goddess can be seen as ultimately all genders or genderless or both.
4: The God and Goddess represent all Gods and Goddesses including Bisexual, Lesbian, Gay and Transgender Gods.
5: There are Wiccans and Wiccan groups who do not use the ” God/Goddess language”. Some use just God or Goddess for example.
6: Sex and fertility rituals usually are symbolic or have a symbolic layer. But they can be alter, changed or left out . In Gay Witchcraft, Chris Penczak offers suggestions on exploring one’s sexuality and gender expression in ritual by taking on different parts in ritual such as a male being the Goddess.
7: There are LGTBQ Wiccan groups who created non-heteronomative covens, rituals and theology.
This is not to say Wiccan community does not have tons of problems as far as heterosexism and cissexism. More that, there are plenty of ways to look at the philosophy/theology and practice in a non-heteronormative/Cissexist way. Plenty of religions fight with oppressive ideas, Wicca is not any different or uniquely doomed.