Opponents to gay self-determination either do not believe that equality of rights can be achieved between heterosexuals and gays living in a same society.
On contrary, they mostly believe that a true equality is possible! The most opponents of "gay separatism" have no hostile motivations, they just do not see the necessety of a separation or do not believe such a thing is possible. For many, homosexuality is just a minor part of their personality - like the color of the eyes, and who are we to judge upon these people? For some of us the issue is more important than for others, few would define themeselve as forming a new-age
ethnos based on their sexuality.
I for my part advocate the queer self-determination, but in the form when queer people and the "gay state" is integrate part of the entire world. There is no contradiction in this - any nation/people can rule upon itselfe, be aware of it's own cultural value and cooperate with other nations/peoples for the mutual benefit.
Sometimes people just misunderstand the idea, they really imagine we are agitating for deportation of all homosexuals against their will to a "ghetto", building a wall around and shoot at anyone who would try to escape. They then start to ask about how are we going to reproduce ourselves or suggest that children might be born and in a couple of generations the heterosexuals would form the majority again etc. While some of the problems seem not entirely artificial (e.g. the "hetero child problem") and inspire us to look for creative solutions, other questions stem from distorted impression over the project. An extremist view like "let's sterilize heteros in the area" can cause much harm as well.

I remember reading an article from Julia Penelope ("Wimmin-and Lesbian-Only Spaces: Thought into action"), where she was fiercefully advocating that lesbians with male children should be excluded from the areas "Only for wimmin", even if the children were just couples of month old. She was deadly serious and really arguing over 2 or 3 pages about the perfidity of lesbians who would disguise their male babys into girl clothes and smuggle them into the "Wimmin areas", just imagine the
danger thei imposed upon other wimmin!!! We should be catious that we do not place ourselves into similar ridiculousness by extreme theoretizing and concentrate our wits on how to include some of our folks in need of protection, rather than to exclude someone because he/she hadn't shown sufficient ideological tightness. The only reason for gay government (likewise gay state) to exist is to gain additional cultural and political benefit for the gay population as whole and for any given gay individuals in particular.
I am confident that once the gay state is really established and the benefits are visible, the support among the community will grow.