Today's understanding of gender differs from that of "sex."
Sex refers to whether a person is male or female, and gender
in today's context, man or woman.
Some post-modern arguments are that gender is a "social role"
that a person puts on because of his sex. That gender is
collection of norms that society expects of a certain sex.
And how some homosexuals look at it, is that they are forced
to put on that social role of being a man or woman regardless of
how they really feel. Thus they question, why is it that they
have to be a man if they are male, or a woman if they are female?
This also opens and links to arguments of gender equality. Being
a woman in the past meant that they had no voting rights, or had a
subservient role in society. A similar question is asked, why
should a female be restricted to the social role of a woman which
carries so much restriction and inequality.
So what is homosexuality? I think it has more to do with a
person's perceived gender and social role that deviates from the
sex-gender norms. An effeminate gay man, may be attracted to a very
"manly" man, or "manly" woman. And if we consider this
plausibility, then gender inequality has very much to do tolerance
or acceptance of homosexuality.
I think there are certain features of homosexuality that
appreciates the "qualities" of the other gender. Maybe being
able to wear make up, or shop for lingeries... or being able to
speak loudly and keep short hair? Maybe some of the social
restrictions are more material? Such as glass ceilings for
women's careers... preference for men in long term key positions
because they wont have to take maternity leave etc etc.
There could be a desire to be like the opposite gender because of
such things.
Hence, there seems to be a correlation between greater gender
inequality, and less tolerance for homosexuals. The reverse
where there is lesser gender inequality, and greater tolerance for
homosexuals may also be true.
Maybe that answers the question to why the most gender equal
countries are seemingly also most tolerant to homosexuals.