Now, I’m a Christian, but I cannot abide by such faulty arguments.

Without a real God that created humanity and provided absolute truth on how to interact with each other for a properly functioning society, then how do you conclude what is actually right in order to do it.

First off, as a social species, humans have evolved to have empathy, giving them an intuitive sense of right and wrong, at least in broad strokes. This empathy is often strongest for those who are most like the subject. We also evolved to have a sense of fairness for similar reasons, which similarly provides guidance to our individual sense of morality.

Second, we can basically come up with a society-wide set of morals by agreeing on certain goals to work towards, like maximizing well-being and happiness for as many people as possible while minimizing harm to as many as possible, and some sort of priority system. Actions that help us approach those goals are “good”, while actions that push us further from those goals are “bad”. Obviously, some of the details are not agreed upon, which leads to gray areas.

Really, that’s basically what morality is: things that progress us towards some goal we like are “good”, while things that push us away from that goal are “bad”. And it can get pretty subjective and relative. Even if we just look at Christian philosophers, there is a lot of disagreement among them because they can’t agree on some things like goals and which things are more important. And there are a lot of gray area and many exceptions to generally accepted rules.

On a side note, playing a different sort of Devil’s advocate, let’s say that there is a real God who created humanity and provided a code of conduct. 1) That’s not an absolute morality as there are still exceptions to some of the rules. 2) It’s also not an objective morality because it’s based on the views of a personal being (God). 3) If it’s so perfect, why has it changed over time? I go into more detail later with some examples, but the morality most American Christians follow today, even the most devout Evangelical ones, is not the same as the one in Biblical times or even in early American history or just a few decades ago. 4) Again, if it’s so perfect and an absolute truth, why is it that so many Christians cannot agree on what that truth is? And what about the other religions with their own rules? What puts Christianity above them?

Since there is no way to definitively prove or disprove the existence of any God, gods, or goddesses in general, which God, gods, or goddesses exist (if any), which of the many holy texts is/are an accurate description of the “true” morality, or which interpretation of the “true” holy text(s) is the right one, if any, until after death, and there is no provable way for the dead to come back and tell us (and the stories of those that claim to have done so or that they witnessed someone else do so) are contradictory or unhelpful in these matters, as a practical matter if nothing else, it’s best to treat morality in general as relative and largely subjective.

For example is sex outside of marriage right

In my opinion, it depends on the particulars. Is the sex consensual by all involved parties? If so, was that consent informed and not coerced? Is either party dating or married to someone else? If so, is the married/dating party’s significant other aware of and consenting to the act? Is this an exclusive relationship (that is, limited to a subset of a relatively small, known group of persons that are also only sexually involved with a subset of that same group) that is just not formally recognized by some sort of authority? If not, or if any sexually involved party(s) may or do(es) have some STD(s), are they taking precautions to prevent the transmission of STDs? Are they taking actions to prevent pregnancy? If not, have they adequately planned for the possibility of a pregnancy, and if so, what is that plan and how well prepared are they for it? What are the ages of the parties? Is there a command relationship between the parties outside of the bedroom? Does this relationship lead to a conflict of interest or favoritism in their professional/political capacity? Has either party vocally condemned sex outside of marriage during or prior to the affair? Did they lie about the affair, and to whom?

I don’t believe there is anything inherently wrong or dangerous about sex outside of marriage, so it depends on the particulars. That actually applies to a lot of statements as broad as this one. The answer to such broad questions is often, “It depends.”

(Note: I personally have no intentions of actually having sex outside of marriage, but I don’t judge the morality of others’ behaviors based solely on mine.)

and if so (going against "God" given rules), how do we know it’s not actually causing tiny undetectable ripples of damage to society that combine with other tiny ripples (like envy, gluttony, pride, etc.) which eventually lead to waves of broken adults later on.

That’s where psychological and sociological studies come in, though it’s also worth noting that it also depends on how one defines “damage to society” and “broken adults”.

We can determine some measurable indicators of “damage to society” and “broken adults” and measure those against the questioned behavior (in this case, sex outside of marriage). If there’s a statistically significant correlation, more studies can be done to determine the likelihood of a causal connection between them and what direction that causality goes as well as the possible existence of confounding factor(s). If so, then we can determine what and how much, if any, “damage to society” is done by sex outside of marriage and, if there is any, how much of it is preventable without disallowing sex outside of marriage altogether. Of course, these studies would have to be compared to sex within marriage and a mixed group of both.

Again, though, this depends on how we define “damage to society” and “broken adults”, which are in turn based upon some predetermined goal(s) upon which to base our morality. It also depends on our threshold for “damage to society” before we determine something is “bad”.

And then there’s what you said about envy, gluttony, pride, etc. Again, those would have to be tested for “damage to society” before we could even determine those to be “bad for society”.

Perhaps our feeble efforts to relax the long established written religious rules of conduct because "God doesn’t exist" is the reason for 99% of society’s current ills.

[citation needed]

First, you presuppose that there are long-established written religious rules of conduct that were followed more often before than they are now. Given the fact that there have been numerous disagreements throughout history on what those written rules actually are even within a given faith and the diversity of faiths throughout history, each with their own written rules of conduct, and the fact that many of those pushing these rules are often guilty of breaking them, this is a questionable assertion.

Second, you also presuppose that there has been an increase in “society’s ills”. Again, I don’t see any evidence of that. There has actually been a decrease over the past several decades in crimes committed in general and in violent crimes in particular. I suppose it depends on how one defines “iils” in this context, but then people can’t seem to agree on that.

Third, you presuppose that there has been a relaxation of the aforementioned rules that is because of people asserting that “God doesn’t exist”. 1) Many religious people have a more relaxed interpretation of the rules than their ancestors did that has nothing to do with other people saying that God doesn’t exist. 2) You assume that religious people are more likely to follow these rules than atheists, and I haven’t seen evidence that this is the case. 3) You forget that sometimes the rules have gotten stricter; for example, slavery used to be condoned, but no longer is; polygamy was once allowed and is actually explicitly allowed in the Bible, but now it’s condemned; racism and sexism were previously commonplace but are now strongly discouraged.