Well, I think that it's unfair of you to automatically throw churches in with the same lot as private clubs, etc. I think the reason private clubs are allowed to exclude certain people is because the function of a club (and I'm assuming night clubs are what we're talking about?) is very dependent on who goes there. The crowd of people, the music, etc. If a club let just anyone in, wearing anything, it would be damaging to its reputation and image.

Furthermore, I think if a club turned away all black people there would be serious problems.

And colleges aren't allowed to pick whoever they want. They have to accept some minorities.

The workplace allows it, to my understanding, because it is discrimination of a severe and harmful brand to exclude employment based on race or gender (and I believe sexual preference).

Race and gender are well outlined bases for harmful discrimination, sexual preference is not. The common thread between race and gender is that discrimination is not permitted unless doing so preserves the expressive message of the private institution. Race, gender and sexual preference in my view often do not affect the expressive message of a workplace, restaurant, or church.

Discrimination is a lot less tolerated than you seem to think it is. I even recall one case being heard about discrimination of parents because a restaurant refused to serve parents with a baby.

Apparently the case has some weight to it, but I honestly don't know enough to say.