Because that's unrealistic? people are different for a number of reasons, not just sexual identity. we should celebrate difference. the argument can't just be 'everyone should be equal'. historical, political, social processes have disadvantaged, marginalised, and abused certain identities over many years (and into current day and on many levels (personal, institutional, systemic, etc.), while it's afforded others privilege. we can't just ignore that and expect everyone to be magically equal.