The reason atheists can (and should) enter into religious discussions and theological disputes, judging religions, is because Jesus, Muhammad, Moses, Krishna, and Buddha do not belong to the faiths to which they are associated.
In the 21st century, these figures belong to global culture. The texts associated with them can be read by anybody in translation and verdicts drawn (and hypocrisies among “followers,” such as Tim Teebow in relation to Jesus, noted). No man is an island. How religious texts are read and interpreted impacts everyone. Therefore, atheists, if they want to be, are properly part of the discussion. It is not ridiculous for them to critique religion and the followers of religion on religion’s own turf and terms.
A Christian no more owns Jesus than a Hindu owns yoga. Below, for example, is a Hindu spiritual practice—yoga—being appropriated by Westerners for, shall we say, other than spiritual purposes.
Are such syncretisms fair game?
Yes.
Why? Because Hindus don’t own Patanjali (or any other early yoga innovator). No religion gets to escape full public view and dissection on the Internet, nor does it get to own how people apply it or what they notice about its (self-proclaimed) followers. An atheist commenting on Jesus’s followers or a Christian commenting on the Nietzschean consequences of atheism are not out-of-bounds or acting absurdly.
Jesus is not the property of 21st century Christians and Nietzsche is not the property of atheists. Because of our inescapable interconnection with one another in the 21st century, the dialogues invariably cross the boundaries set by earlier, more isolated, historical eras.
Prometheus Unbound 
good post… have a read http://bizzareness.wordpress.com/2012/01/11/67/
All due respect, Santi, but David Silverman was not merely entering into a “religious discussion” with Tim Tebow, nor simply inviting the wider Christian community into theological dialogue on the issue of public prayer, nor was he merely offering an opinion. Silverman was judging Tim Tebow — as were you, I’m afraid — and doing so based on a misreading of the Bible. Properly interpreting the Bible can be tricky, and is often dependent on knowing the historical and cultural context in which it was written. Matthew 6.5, however, is hardly one of those texts; its intent is quite clear. So, when an atheist misunderstands a passage of Scripture, then uses it to openly and unfairly criticize a very visible and public Christian, and then judges that person — and anyone like them — as either egregiously ignorant of their own faith, or as a horrible hypocrite, you’ll forgive me if I find that not only wrong, but that it evinces more than a little presumption.
The presumption is also on your part. The Bible does not belong to Christians; it belongs to all of humanity. We can all read it and interpret it.
And you assume that you are giving Mat. 6:5 its proper context and emphasis, but you have not told me what you think that context actually is. Please tell me why Jesus didn’t mean what he said. What is this crucial interpretive context that you think I’m dropping with regard to the verse. I’m happy to change my opinion of the passage if given a convincing argument.
—Santi : )