Yeah, I'd rather sexuality wasn't on the forms. The rationale, I believe, is to track it for counter-prejudice systems. Which is to say, assuming society has a level of prejudice that results in people being denied jobs they should have. By requiring a level of hiring of the prejudiced-against parties, it counter-balances that prejudice until such time as the prejudice is effectively removed from society and so restores the balance of employees you'd see without that prejudice. Not a perfect system, but I'm pretty sure that's the logic.
Except most the 'liberal stuff' seems to be mostly reacting to when the issue gets forced. "I want to get married to the person I love", "Can't. Both of you have cocks.", that sort of thing.
Or combating systemic prejudice, when a system is weighted against specific parties based on arbitrary grounds like sexuality. When the police are much faster to shoot a black person to a white one, for example. The issue is being forced by the nature of that system, even if not explicitly and openly stated by the police in question.
Also, hey actually relevant:
http://www.bbc.co.uk/news/world-us-canada-38853350Responses to Trump's "dress like a woman" policy:
I'll dress like a woman when you act like a president, police officer tells Trump