This is an example of where the MCAT can have more than one right answer but one is more right than the other. While individual prejudice can help encourage people to become more open with their sexuality, when identifying themselves as such, think of instances like filling out a form. It doesn't matter if your friends and family support you, you're not going to check "identifies as homosexual" if you think doing so will affect you negatively in society. So removing institutional stigma will likely increase identification of sexual identity.