If I were conducting interviews for a lighthouse guardian-type position, I would be fine with hiring a Nazi zoophiliac bug-chasing rapist with a scatological fixation and a fondness for Beck's beer, as long as he could do the job well. Arguably, I might even be somewhat happy to have a chance of reducing the social presence of such a distasteful person.
But if I were hiring a personal secretary, I (or whoever they will work with) would need not simply to tolerate, but to actually like the guy or gal. Good personal chemistry is a key part of that job, and if there was a law forbidding me from discriminating against, say, Scientologists I'd make a serious effort to circumvent it (hardly a difficult feat; I probably wouldn't even have to lie).
Other jobs fall somewhere in the spectrum between those two extremes, and would be treated accordingly.
Admittedly it might be because I have (very mild) autism, but as long as a personal secretary was sufficently competent I wouldn't mind if I didn't get along with them.
Let's say you are interviewing a candidate for a job. In casual conversation, the candidate mentions that he is a member of a rather old and prestigious country club. You've never heard the name of the club before.
You look up the country club afterwards, and are surprised by what you read. The club refuses membership to homosexuals. It revokes the membership of couples who use birth control. Leadership positions are reserved to unmarried males.
The candidate is otherwise competent. Under what conditions would you hire him? Would you want a law passed banning hiring discrimination based on country club membership?
(The country club is analogous to a nicer version of the Catholic church. I left out a couple bad things.)
Religious discrimination is illegal in many parts of the world, and I think that's probably a good thing. Still, keeping this at the object level (no meta-rules or veils of ignorance) it seems to me that discriminating against religious people is fine. I'm curious what other people think.