If an employer was a discriminating kind, they'd already have access to a lot of information they would need, even without the internet.
Your sex and race are instantly apparent, age and many disabilities can be guessed, national origin can be figured from an accent, and marital status can be seen by looking for a ring. Even religion can be discerned in some cases, for certain orthodox members.
I agree that employers being able to easily see an employee's sexual orientation might not be a step in the right direction, but I don't think it's opening up a huge can of worms. It's an already opened can of worms.