but now that I think about it, this is only really a protection if you’re already hired at the place. If you just slam the door on people before they can get in, discrimination seems to be legal.

Pretty sure that protection so applies to the application process. Can’t have places rejecting every non-white candidate for being the wrong race. The problem is proving that you were rejected for a BS reason is really hard because they usually don’t flat out say it, and especially not in writing