Hmmmm. . .that would also be true of the letter from Jefferon that is often sited re: separation of church and state. And yet, the liberals never seem to mention THAT is "only a letter."
Instead of liberals, I think you mean atheists. In general (and I've been on LOTS of atheist/Christian argument lists) most atheists use it as one evidence that not all the founding fathers were Christian.
I'm certain even you can see the danger in allowing government to be used as a means to advance one's religious dogma. The religious dogma of officeholders may not always be consistent with your own.