Well, the obvious answer from my perspective is that...No, you don't know you are right. No one does. That is why it's called "faith". There will inevitably be people who come here and present "evidence"...but there are a whole lot of scientists and atheists and scholars that have great "evidence" as well. No one can prove or disprove anything. We can't concretely prove there is no Santa Claus. But somethings are just ridiculous and go against our logic.
That in addition to all the other religions you mentioned...there are so many idea's out there. Once you see that christianity is just another one in the mix...it all starts making sense.
This is why I am atheist/Satanist.
Religion forces you to suppress cognitive thinking skills. Anyone that know's anything about psychology can see how all religion is basically brainwash. Your parents introduce whatever religion it is that they are to you and they (along with schools and a lot of other forces) work on you until you are one of them. It doesnt work on everyone, but it does on a lot of people.
That's a biased analogy, but I agree with it in part. I have a Chinese friend who believes that the Party brainwashes Chinese people into believing in atheism. Did I mention he's an agnostic, himself? Rather than accepting the Communist Party's word on God he's begun to start asking questions about it, himself.
So does brainwashing occur? Yes. Can a person be brainwashed into believing a lie? Yes. Can they be brainwashed into believing a truth? Yes. It's called deprogramming. So does brainwashing have any effect on what the truth is? No. So such an argument for being brainwashed into believing a religion or lack thereof has no bearing on the actual truth.
Religion also does not force you to suppress cognitive thinking skills. Aristotle once purportedly said, "It is the mark of an intelligent mind to be able to entertain a thought without accepting it." Do I have doubts? Sometimes. Do I just blow them off? No, I often debate with myself to explore the veracity of ideas. And I've arrived at the conclusion that since we will not have definitive proof in our lifetimes the best belief is the most logical belief. Is Buddhism a logical belief for me? No, because it uses deception. How can I believe in something that professes to deceive to achieve its goals? Is Santa Claus a logical belief? No, because there is evidence to show his origins. Is Satanism a logical belief? Probably not as logical as Christianity on which it depends.
Is Egyptian sun-worship logical? No, because we all know that there is no Kephri rolling the sun around in the sky like a giant ball of dung.
Is Christianity logical? Archaeology continues to prove the Biblical account of history, and while prophecies may be open to interpretation there is also strong evidence for them from the Bible. If they were completely inaccurate then there would be no other interpretation for them except for "they have not come true yet" or "they are false." Is there evidence for Jesus? More evidence for him than perhaps other historical figures commonly held as fact. I'm not going to question Aristotle's existence unless I have some reason to disprove him, but I'd be willing to bet there is much more evidence for Christ than for Aristotle (everything from the Pilate inscription to the geographic spread of Christianity from a region in which Christianity would have been the most difficult to come from if the Gospels were fake). So is there something for atheists to gain in trying to disprove Christ?