Since the OP did not provide some examples, I'll go ahead and give a few (and ride on a few examples already posted.)
My relative recently deconverted from Christianity and in discussions with her friends who still believe, a few interesting points cropped up, namely in the area of the term 'faith' and its definition. Her view is this: 'faith' is nothing more than a synonym for 'really really wanting something to be true' but not wanting to admit otherwise'. And I'm sure you'll agree this is the typical view of the world (when they look at religion from the outside.) After all, you never hear Christians say 'I really really hope Jesus will return'. This can be shown in other examples, i.e.:
- Jews having faith that they are God's chosen people.
- A husband having faith his wife will recover from illness.
- A group of Muslims having faith that blowing up the twin towers would grant them entry to heaven.
My examples are wide-ranging because I want to focus specifically on the term 'faith' and its validity. To appeal to external evidence, i.e., the empty tomb, is missing my point; to give faith as a condition at all implies that it is a valid concept. But if faith is nothing more than a heavily glorified wanting, what makes the Christian faith more valid than the examples above?
First, to comment on the examples:
- Jews having faith that they are God's chosen people. - But they failed to realize that their Messiah had come. Identity as God's chosen people is based on covenant (as even they agree -- see the centrality of Abraham, Moses, and David, the three most famous covenant heads), and by rejecting the Messiah they were rejecting the covenant. That is to say, this is not faith in a person but faith that a proposition is true, and that proposition must be revised according to information which they have rejected.
- A husband having faith his wife will recover from illness. - This is optimism, not hope. But optimism has no place in a world where Jesus attains the ultimate victory by enduring suffering and martyrdom. Christian hope is grounded in a trustworthy person who has made beautiful promises about the future which provide us with hope, not optimism.
- A group of Muslims having faith that blowing up the twin towers would grant them entry to heaven. - The way it is being portrayed, this is just a blind wish and not the trust of a perfectly reliable person who has made sure promises.
But your complaint might be of this form: "I have faith that Christianity is true" doesn't necessarily end the conversation, because there are a lot of people who say "I have faith that x" and yet are obviously deluded. I agree with that. "I have faith that Christianity is true" doesn't constitute an end to dialogue.
For instance, our faith is all rubbish to the world. But we don't define 'faith' the way the world sees it. Faith according to the bible is very different.
Faith isn't really wanting something bad. Its belief it will occur. There is a distinct difference. What makes faith valid? The accuracy of what that faith is in.
For this discussion, there are two definitions of faith: the world's and the Bible's. If there are discrepancies in this statement then please ignore it. The basic idea is the definition that anyone knows of is the world's. The Bible's is much different:
Heb 11:1,6 Now faith is the assurance of things hoped for, the conviction of things not seen. And without faith it is impossible to please him, for whoever would draw near to God must believe that he exists and that he rewards those who seek him.
Actually, I would have to say that the common definition is more about hope than faith in that hope is more oriented to the future and is grounded in faith. I would put it like this: I believe in "something" and so therefore I also believe that whatever happens in the future is grounded in that "something". Just substitute God, or even better, the promises of God, for "something" and I arrive at the idea that because I have faith in God and that He has made certain promises then I have hope, or confidence, that what He says will happen in the future will happen. All of this is grounded in the knowledge that God has in the past made other promises that others have believed in and they have experienced those promises for themselves.
But the popular view of the Christian faith is that it can't be based on any evidence or reason -- that's basically what we're all saying. This idea seems different from what I read in scripture. There are plenty of people who believe after seeing miracles or works of Christ. Thomas believed after witnessing the resurrection. He missed out on a blessing by having to see the Lord before believing, but his faith was still faith. Faith in the Bible is trust in God, and particularly in God's promises, and has little or nothing to do with an opposition with "reason" -- unless "reason" means "trusting in myself alone," I suppose, which it seems to for Descartes and his descendants.