Hey, I said I didn't want to start an argument! But now I have to respond. ;)

I think these "extreme atheists" you're referring to are atheists only as a kind of side detail. What they really are at core is "lost sheep looking for a flock", and when they think they've found their flock, they try overly hard to demonstrate their belonging. Basically, they're console fanboys who happen to have chosen Atheism as their totem rather than the PS3, or whatever. Plenty of "extreme christians" in this category, too. I can't just hand-wave them away, but hope you can agree that their behaviour most likely descends from causes outside the putative core of their argumentative focus.

"Everyone has some ridiculous/irrational beliefs. I believe that everyone is entitled to their irrational beliefs – whatever they may be."

They most certainly are. However, when they graduate from privately harbouring whatever beliefs they have to trying to change the world and others to suit, that's when I, and a great many others, start to have a problem with it, and tend to see the belief as the cause.

This is so common I probably don't need to give one, but a great example was the constitutional amendment last year to ban gay marriage in California. What a stupid, pointless, hateful thing to do. And all because of these "ridiculous/irrational" beliefs. Don't seem so harmless now, do they?

"My point is that the CC did and still do some very good work for people"

I know the Catholics have built their share of schools and hospitals. I'm a pragmatist, outcomes are what matters, and the truth that if we absolutely had to choose a religion, any religion, we could certainly choose worse than Catholicism.

However, making such points is kind of useless. We have no way to know how many hospitals would be in Africa absent the CC. If the whole world had moved to enlightened atheism in the 1950s, would there be more or less schools in Africa? If the scourge of religion had been scrubbed from Africa decades ago, would it even need us to be building its hospitals for them?

All interesting but unanswerable questions. Yes, the CC has done positive things. Maybe even as many good things as bad things. So? Doesn't make their Interdimensional Space God any more findable, and their attitudes towards eg. Third World contraception remain utterly comtemptible. Would the world be a better place, on balance, without the Catholic Church? I suspect

"Let everyone believe in their own irrational beliefs. My father does not believe in evolution – yet he is one of the nicest people I know. My sister believes that Jesus wants her to work with orphans. What harm does this do to anyone?"

I wish you hadn't written about your family, since it makes arguing with you akin to insulting your loved ones. However, now I have no choice.

Superficially, there's nothing wrong with the situation as you describe it. The problem is that there is irrationality and mysticism embedded in this system and it can quickly go off the rails. Your sister might be helping orphans today because "Jesus wants her to", but tomorrow "Jesus" might tell her to persecute gays or bomb an abortion clinic. Once you accept that taking orders from imaginary friends - or their supposed representatives on earth - is OK and valid, how can you argue when those orders swing to an activity you don't agree with?

And if your father really, truly believes that evolution is false and wrong, he must be very angry about the malicious lies being propogated at this very moment to innocent children in schools all around the world. Is he campaigning against that, then? If not, why not? Maybe his level of conviction will go up one day, and then he'll start? What will you think about his "harmless" beliefs then?

If you accept, even encourage, magical thinking at times when it seems to be doing no harm, it makes it very difficult to reject later on when the activities of the "faithful" turn counter to what you know to be the best interests of society and humanity. This is folly. Logic, reason and evidence-based thinking are the only valid means to reach any decision, take any action, form any belief. Magical thinking is the sworn enemy of reason and logic, and must be defeated whereever it exists. If your father and sister experience a rude awakening as part of that wholly correct process, well - as adults, equipped with brains capable of thinking just as well as anyone else - they should have known better.