This has already been mentioned in the thread, but we don't all believe that our own religion is the one true one. It's one of the reasons I can still call myself Hindu, actually.
Admittedly, I don't know much about Hinduism, the result of an educational system that was 99% Catholic, 1% everything else. But when I talk about religious types that insist that their religion is the only true one, I'm referring to quotes like this:
I'm a "Christian" if you want to put labels, the Bible is the word and truth of God and through Jesus is the only way to salvation.
See, followers of Mohammed think differently. Jews too. And Hindus. In fact, pretty much all the non-Christian religious groups disagree that Jesus is the
only way to salvation. In fact, different Christian groups can't agree on the way to salvation, with some believing that having Jesus as your saviour is enough, other believing that good deeds are required, and some thinking that undergoing certain sacraments is essential to reaching the afterlife... They can't all be right.
That said, I also feel that the utter fragmentation of religion is one of the main reasons in favor of the endeavor. I've never been a fan of the "one size fits all" mentality. Just as I can't believe that one political or social or cultural lifestyle can appeal to all people, one religious one can't either.
I don't believe that one political or social or cultural lifestyle can work for all people either. But religion isn't just some cultural thing, it is an attempt to explain the great mysteries of existence, to provide answers to the reason behind life and the very universe itself. To those questions, there can be only one truth. Humans could have evolved unaided, or their could have been a god that aided the course of our evolution, or there could be a god that just designed humans directly and made it look like we evolved. I can accept that there are multiple viewpoints on what really happened, but in the end only one of those viewpoints can be the correct one.
Jesus could be the one true saviour, but why do his followers disagree on so much of his message? Was he not clear in his words? If he was clear, why the sectionalisation? If he wasn't clear, how can you be sure that Catholicism is the closest interpretation of his message? How can you be sure of his message at all?
(Sorry if I appear preachy, I'm not trying to convert you or anything, I'm just trying to explain my thought process.

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There's only three options with Jesus:
1. He was the messiah.
2. He was a liar.
3. He was nuts.
4. He was a nice guy whose message was dressed up by those that came after him, including the addition of stories and concepts from other religions, in order to reach a wider audience. Would you be more likely to listen to a message from some hippy or from
the son of God? (I wouldn't listen to either, but I'd go out of my way to ignore the hippie.

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