Others could speak up too, but I think you'll have a hard time finding support for that position among anyone who calls himself a libertarian.
Why do you think a business owner should be controlled in such a way? Specifically, what makes a person different once he's an employer, such that he loses some of his rights? For example suppose you decided to sell your car, or buy a new VCR. Should the government get involved in that transaction to determine whether your decision of who to buy from, or sell to, was based on politically acceptable criteria? Employment is simply a business transaction in which the employer buys labor from the employee, nothing more.
How does an employer prove that he's not discriminating? How does the government determine that he is?
Is it okay that Hooter's only hires women as waitresses?
You don't have to answer all these, just stuff that comes to mind.
I really like how you expain your position here. Very clear and concise!