I typically start by pointing out that several of the founding fathers were deists; and several viewed religion poorly in general. Then ask them to state the principle basis for first leaving England (Europe), and then for declaring independence from England.
For a good counter-point on the christianity claim, ask them to list all the places Jesus is mentioned in any of the founding documents. Specifically Jesus, not just God.
Next the inevitable claim comes that it was based on the Bible, or that our laws were based on the ten commandments. Then you ask them to list all the places God appears in the founding documents; and followup with listing how many of the commandments are actually laws.
Usually they throw in "under God" from the pledge, or "In God We Trust" on money, or as the national motto. For these have them research when those were added, and they can see these were not part of the founding.
If you haven't convinced them (or shut them up) with this (or points like these), you probably will never convince them.
...well, you can argue against the claim by giving examples of values that Christians think are supported by the Bible but aren't. One is slavery. As Americans, one precept we hold dear is that owning other human beings is wrong; a lot of Christians claim it was because of Christian values that we went to war and freed the slaves. NOT TRUE! There is not one sentence in the Bible, OT or NT, that says there's anything wrong with slavery. My mom tried to say that slavery was like employment back in the day, but that's a lie and a delusion... especially since the Bible goes a step further and details how to beat slaves and discriminates between TYPES of slaves (and whether or not they're Jewish... Jewish slaves are to be treated more humanely and eventually set free). Jesus instructed slaves to obey their masters and masters to treat their slaves well, but he said nothing about setting them free or considering them employees.
If America were founded on Christian values, we would own slaves.
Also, Women's Rights shouldn't be considered a part Christian values. Even though Jesus sympathized with women more than his Jewish counterparts, he could have gone a step further and stated that women should be treated as equals. If we lived according to Biblical standards, women shouldn't speak in church or in public at all (and this is according to Paul). There are a lot of women who preach, which seems very ironic to me.
No need to debate. I find that the best approach to dealing with people who hold odd beliefs is to ask them simple questions. Generally, you can demonstrate their lack of knowledge on the subject through your own curiosity.
Just a couple to get started:
What are Christian values?
How do you know that the country was founded on them?
Who were the founding fathers?
Asking simple and sincere questions usually quickly leads to a chasm of ignorance below their shallow, yet passionately held, viewpoints. It is quite uncomfortable and undeniable when they are an unwitting participant in the demise of their own assertions. I find it to be much more effective and satisfying than going on the offensive, debating, arguing, making my own claims, trying to educate them, etc.
People find it easy to defend their beliefs. The hard part is explaining them.
I always see answers to this question that list what religion the Founding Fathers were a part of. That's not even all that relevant. The real issue is in finding values that are supposedly "Christian" that were not actually adopted from earlier belief systems or incorporated over the centuries from outside sources. All the values that people claim are Christian are simply values that have been around for a long time and are parts of other religions as well or they weren't conceived of as some extension of God's commandments, but as good ideas that worked in any society. If someone could come up with a wholly "Christian" value, I'd be flabbergasted. If that value were a part of the plan for the founding of this nation, I'd eat my hat.
You're absolutely right. No one can name those "Christian values" on which we supposedly founded this nation.
A very good point, Stacy. "Do not kill" is one that they like to trot out as an example of Christian values that are incorporated into our law, but it's hardly a value that is exclusive to Christianity. Christianity incorporated that value into itself, not the other way around.
The most common argument for us in this kind of debate is the Treaty of Tripoli, written in 1796 most of our founding fathers were in the senate and just so happened to unanimously approved it. Contained this gem:
"Art. 11. As the Government of the United States of America is not, in any sense, founded on the Christian religion; as it has in itself no character of enmity against the laws, religion, or tranquillity, of Mussulmen; and, as the said States never entered into any war, or act of hostility against any Mahometan nation, it is declared by the parties, that no pretext arising from religious opinions, shall ever produce an interruption of the harmony existing between the two countries."
The "values" that the founding fathers wanted to enshrine in our early government were enlightenment values. Values which stood mostly in direct opposition to the religious authority of the recent past.
I like asking what is the first commandment and what is the fist amendment.
Thou shall hath no other god before me vs Freedom of Religion
Tom Leykis (radio) used to do a bit called Ask the Atheist. When the claim of the US being founded on Christian values came up he'd run through a list (expounding Cara's thought on Christian actions) Genocide, Theft of land, subrogation of women, Slavery, witch hunts, public executions, internment camps... Which Christian values would you like to claim credit for? Sit back and let the Benny Hill music begin.