The Pugnacious Irishman considers the general objection:

No one can prove God’s existence (or Jesus’ existence, or that the Bible is God’s word, etc, etc…just toss in any number of Christian staples).  There is no evidence whatsoever.  It’s all belief and faith.

This is called hard agnosticism. Atheism is the claim “There is no God”. Soft agnosticism is the claim “I don’t know if there is a God”. Hard agnosticism is the claim “No one can know whether there is a God or not”.

Now take a moment and think about how you would respond in a general way, without plunging into the arguments and counter-arguments.

Rich begins by teaching us about the notion of burden of proof:

It is important that when someone says that to you, that you never let them off the hook.  It is just too easy to throw it out there without backing it up.  It is a particularly convenient one liner for those who aren’t really interested in God and for those who have not thought deeply about God.  That’s not to say that everyone who says that hasn’t thought deeply about God, it’s just that it’s easy for folks like that to resort to it.  Rather than launching into disproving the “no proof” belief, force your conversation partner to shoulder his responsibility: he made a claim, now he must back it up.  No reason for you to launch into Kalam mode.

This actually happened to me when I was working for a software company in Chicago. We were waiting for a meeting room to empty. I was browsing a William Lane Craig debate transcript on one of the lab machines, when one of the engineers said, “Why do you read that stuff? No one can know whether God exists or not!” So I said, “Why do you think that?” And he said, “Because God is non-physical and that means that we can never have evidence of a non-physical entity”. And we went from there, straight to the Kalam argument.

Rich documents FIVE responses here, and breaks them down. My favorites are the last two, but they are all useful, depending on the person who is asking.

By the way, here is the evidence for Christian theism and responses to objections, if evidence is really required. But the point of this post is that if anyone makes a claim to know that there is no proof that God exists, the first questions you need to ask before you go to the data is: what do you mean by “God”? what would count as proof for you? who have you read? what is wrong with the arguments that you’ve read? Etc.