Voted up for an important topic.
I thought you were going to go the other direction here -- one man's modus ponens is another's modus tollens.
In other words, if we tolerate Catholics, we should tolerate holders of other opinions that we find equally outrageous and offensive -- explicit racists, for instance. Here "tolerate" means something less than "agree with" but more than "refrain from throwing in jail" -- it means we should associate with them, offer them jobs they're otherwise qualified for, etc.
There has to be some mechanism for sharing a society with people whose opinions seem truly horrible to us. We seem to do this naturally when it comes to religion, perhaps because we have a three-hundred-year-old tradition of religious toleration. But toleration more broadly is a difficult thing and it's not always obvious how far it should be taken.
For instance, for all I said above, I probably would not date someone whose beliefs bothered me (and yes, this includes devout Catholics.)
There has to be some mechanism for sharing a society with people whose opinions seem truly horrible to us.
This is something very important. Too many people confuse tolerance as meaning being nice to people I like but bother some other misled ignorant soul. Tolerance as something useful to society is being civil and fullfining obligations set down by the social contract with people you don't like but that otherwise fulfil their obligations.
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.