Do All Religions Add Up To The Same Thing?

I am reading through The Reason For God by Tim Keller and, to help me take in what he says, have decided to post what I learn from it.

The first chapter addresses the statement There Can't Just Be One True Religion. In it he looks at some things that have long troubled me and has helped bring clarity and reassurance. Here's the two doubts that he helped me with the most.

We are conditioned to believe what we believe so how do you know what you believe is true?

This has been a niggling doubt that reoccurs for me every once in a while, perhaps because when people come out with this they always sound so sound intelligent and convincing. But, as Keller points out, if this is true, then surely the people who believe this only believe it because they are conditioned to as well. How do they know that they haven't been conditioned to think that and some other belief is actually true? While this doesn't prove Christianity it doesn't disprove it, though many perhaps think it does.

It's arrogant to claim that your religion is only true one as they are all equally valid.

Again, Keller says think about that. If it's arrogant to say that you are right and other people are wrong, then isn't it arrogant to say that the above is right and anyone who believes otherwise is wrong? The people who believe the above have a religion, whether they like it or not. They have a view of God and how to get to Him (or her or them or it, depending on where they stand), it may not be clearly defined but a view none the less and they will contradict those who disagree with it. So what's the difference in making the above claim about God and making the claim that there is only one way to God? They are both views about the nature of God, neither is more humble than the other, although how it is articulated can be.