Why the "There are so many interpretations of the Bible" claim is confused

[Delicate]

Your response creates an interesting set of conundrums for atheists.

Firstly, your view that "If Christianity is true, then it still should not influence culture, as this is a secular nation." This betrays a fundamental misunderstanding of what secularism is, and its status in the light of the truth of Christianity. Secularism does not entail that religion should have no influence on culture. Rather, strictly speaking, secularism entails that religion should have no influence on the state. This means governance should not be influenced by religion. It says nothing of culture in general, and secularism of the state is perfectly compatible with a highly religious, and highly-religiously-expressive citizenry. So you're operating under an idiosyncratic definition of secularism.

Second, if Christianity is true, then it must be true that there is an afterlife, so to speak. And one's well-being in the afterlife and relationship with God is of utmost importance. Someone who concedes that Christianity is true (even for the sake of argument), will have to concede (once again, for the sake of argument) that the latter two theological notions follow. In fact, one might make the claim that it is an ethical obligation to care for one's afterlife and relationship with God. Thus for an atheist to hold that Christianity is true AND Christianity ought not to have any influence on society is unethical and irresponsible towards one's citizenry, to the same extent that preventing people from access to healthcare and freedom, and the pursuit of happiness would be unethical and irresponsible in our current system.

So there are two big problems for your view: Secularism doesn't entail what you believe it does, and you are endorsing an unethical and irresponsible position that harms the citizenry. What can you do to resolve these two problems? Here are what seems to be your two options:

1) You either affirm the view that religion should have no influence on culture (perhaps you can call this view hypersecularism, as it is much stronger than conventional secularism), or you can reject the view that religion should have no influence on culture, and endorse ordinary secularism.

2) You have to either reject ethics (in which case you are permitted to harm the citizenry by constraining Christian cultural influence even if it is true), or you can affirm ethics and allow a cultural place for Christianity, given its truth.

There are more questions to raise, obviously. One concerns the worth of secularism in a world where Christianity is true. Another is the question of the reason and evidence motivating secularism in the real world. Yet another is the question of what normative standards are being assumed without argument when one says Christianity ought not x, culture and society ought to y, etc. 

But I like to keep the conversation short and snappy, so I'll end it here.

There is only one term for the entire basis of this response: delusional.

I can show you why in two easy steps: 

1) Replace what you said, above, with any other religion, such as Islam:

This betrays a fundamental misunderstanding of what secularism is, and its status in the light of the truth of Islam. [...] Second, if Islam is true, then it must be true that there is an afterlife, so to speak. And one's well-being in the afterlife and relationship with God is of utmost importance. Someone who concedes that Islam is true (even for the sake of argument), will have to concede (once again, for the sake of argument) that the latter two theological notions follow. In fact, one might make the claim that it is an ethical obligation to care for one's afterlife and relationship with God. Thus for an atheist to hold that Islam is true AND Islam ought not to have any influence on society is unethical and irresponsible towards one's citizenry, to the same extent that preventing people from access to healthcare and freedom, and the pursuit of happiness would be unethical and irresponsible in our current system.

2) Now imagine having this exact conversation with a copy of yourself from that other faith-tradition, which instead dominated U.S. culture!

Secularism is the principle that religion is a private thing and that government must be neutral with respect to all religions. If we treat all religions as equals, then we can never allow one to gain dominance over the culture; this is especially true in a democratic republic, where the people's culture influences the vote, and yet the representatives of the people must represent all of us, not just the religious majority.

The "worth of secularism in a world where Christianity is true" is proved in the above word-replacement thought exercise. Because we cannot, in reality, know that one group of people's faith is true while all the others  are false, we must be neutral with respect to the claims of all religious persons, must treat them all as equally unsubstantiated. Otherwise, we get Muslim ideals, and talk about how it would be "unethical and irresponsible towards one's citizenry" to deny people the "truth of the Holy Qur'an", or whatever other religion gains dominance next century. That includes yours.

When you make statements like, "You have to either reject ethics (in which case you are permitted to harm the citizenry by constraining Muslim cultural influence even if it is true), or you can affirm ethics and allow a cultural place for Islam, given its truth.", it tells me that I am right to fear you, and your kind. 

So to answer your questions, yes, I do feel it necessary to "constrain" people of your ilk from trying to spread such insidious notions among the cultural and legal institutions by which you might coerce people into joining your private faith tradition. If you wish to practice your faith to the fullest extent your life can permit, fine... but it is clear that you are so arrogant in your religious beliefs that you cannot even see that there might be a world in which you are completely delusional, and your religious claims hold no more weight or moral guidance than any other religion on earth. The True Believer™... and that is what makes you dangerous to the rest of us, atheists and pagans and Sikhs and Hindus and Muslims and Buddhists and everyone not of your ilk included.

I don't think it's delusional so much as you simply don't understand what conditional statements are or how they work.

If Islam is true, then in fact everything you've said about Islam still follows. I can affirm the set of statements about Islam, even if I'm a Christian, because that's how conditional statements work.

I just wouldn't affirm the conditional's consequent in the real world because I deny its antecedent. You don't have to "fear us and our kind." You just have to understand basic formal logic and the structure of conditional statements.  

As for secularism, it's good to see that you've corrected your definition now ("that government must be neutral with respect to all religions"). Unfortunately I still disagree that it denies one religion to gain dominance over the culture. So long as the dominance is not government-endorsed, and is an organic cultural development, secularism has no problem with it. A hypersecular government that intervenes to censor, interfere with, or restrict culture is an onerous burden- look at the Soviet Union, North Korea or Communist China to see what kind of view you're endorsing. 

On the other hand, I'm comfortable with notions of secularism that give people freedom to live their lives as they choose. So let's agree to disagree there.
 
So, what are the salient issues that arise in this discussion? I see three: (a) Learn logic, especially how conditionals work, and (b) notice that a lot hinges on the truth of the given views, be it a particular form of theism, or atheism. If it can be proven that, for instance, Christian theism is rationally tenable, or that atheism is rationally untenable, then that's going to have very important implications for our perspectives. And finally, © learn to subject your views, such as your fervent and whole-hearted adherence to secularism and atheism to the same kind of freethinking, skeptical scrutiny as you subject religions to. 

Secularism and atheism don't get a free pass. Be consistent with your skepticism.