There are a lot of countries around the world that are more religious or less religious than the USA. Finland, Sweden, Denmark, France, Germany, etc. are all far less religious; Indonesia, Brazil, Yemen, etc. are far more religious*. This should pose a natural experiment of sorts. In countries that are less religious, we should see more anti-christian bigotry, more “moral relativism” (I’m not sure what you mean by that, honestly), and more hatred of Christian biblical principles.
We can test this. We can also test whether these amount to bad things - whether countries that are more or less religious are better or worse places to live. Do you think this is a useful or valid test?
*I’m trying really hard to pick countries that are advanced and successful here, but there really aren’t that many first-world countries above the US on the “importance of religion” scale - which should be a bit of a hint as to how this test will go. 
Do the moral laws in the new testament include the ritual laws of the old testament? I’m not sure what you’re about to say, and that’s the important part. Your answer to this question doesn’t particularly interest me that much - the point is that I’ve heard different answers from different Christians. The issue of what even qualifies as “moral law” is not clear. Like most things in the bible, you have to interpret it, and different sects of Christianity have different opinions on what it means. Some issues there is reasonable consensus on, but even on the issue of same-sex marriage, Christians seem to be splitting. These are questions without easy answers, and where there is quite a lot of discord within Christianity.
You know what the most interesting thing about this is? I could advise you to “get your house in order before speaking for Christianity”, but if you did, if all of the Christians in the US got on the same page about what agenda they want passed, they would form a permanent supermajority capable of passing basically whatever they wanted. Any candidate running on the platform of “I speak for the consensus Christian view” would get 70% of the vote in the national election and at least 50% of the vote in over half of all state elections. Christians, could they agree on what they wanted, would control every branch of government with enough power to reshape the constitution however they pleased - so we wouldn’t have this issue to begin with. (In fact, they kinda do.) The problem is not just “atheists disagree with Christians”. It’s also “Christians disagree with Christians”. Or why do you think there are 33,000 different Christian sects? It’s the classic joke all over again:
Once I saw this guy on a bridge about to jump.
I said, “Don’t do it!”
He said, “Nobody loves me.”
I said, “God loves you. Do you believe in God?”
He said, “Yes.”
I said, “Are you a Christian or a Jew?”
He said, “A Christian.”
I said, “Me, too! Protestant or Catholic?”
He said, “Protestant.”
I said, “Me, too! What franchise?”
He said, “Baptist.”
I said, “Me, too! Northern Baptist or Southern Baptist?”
He said, “Northern Baptist.”
I said, “Me, too! Northern Conservative Baptist or Northern Liberal Baptist?”
He said, “Northern Conservative Baptist.”
I said, “Me, too! Northern Conservative Baptist Great Lakes Region, or Northern Conservative Baptist Eastern Region?”
He said, “Northern Conservative Baptist Great Lakes Region.”
I said, “Me, too! Northern Conservative Baptist Great Lakes Region Council of 1879, or Northern Conservative Baptist Great Lakes Region Council of 1912?”
He said, “Northern Conservative Baptist Great Lakes Region Council of 1912.”
I said, “Die, heretic!” And I pushed him over.
Here’s a question for you whose answer I actually am quite interested in - why do you think there are so many disagreements as to what God actually wants from us?
So how 'bout you figure out what that is and convince every other Christian to work with you on that? Because at that point you don’t need a single vote from anyone who is not a Christian, and probably not even a single vote from anyone who isn’t highly religious to boot.