Actually, lesbian theory is a real subset of radical feminism. It has very little to do with attraction and is based in social and political statements.

Lesbian theorists very rarely suggest that all women are attracted to each other - the theory breaks down more like this:

In a patriarchal society, men and women start off on unequal ground, where society is male-normed, male-centered, and male-defined, which disadvantages women socially and politically (radical feminism). The pervasive nature of this systematic inequality deeply affects our interpersonal communications. Interpersonal relationships cannot exist outside of patriarchy, so women can only truly experience a equal, fair, totally loving relationship (the focus being on the emotional much more than the sexual) with other women.

Additionally, some lesbian theorists add that this is a radically transformative move - women existing without the need for men subverts partriachy and helps break it down.

Yes, this is an actual theoretical discipline (with scholars such as Adrienne Rich and Audre Lourde) - it is much more than just a "all women are bisexual theory."