Things like sexual orientation, gender identity, even religion to some extent, aren't obvious in routine transactions, and we can't become a society where everyone is required to wear their color-coded star in public so that the "authorities" can sort out the winners from the losers.
-PJ
They were meant to protect specific classes regardless. An unforeseen consequence of those laws is what happens when protecting one classes rights violate another classes rights. Which one wins? Does opening a business and catering to the public mean that you voluntarily forego your own protections? If the answer to that is no then anti-discrimination laws are unconstitutional.