Lernaean

Your conclusion was that "It is hard to determine what is natural." The whole point of your argument seemed to be to prove that it's hard to define the concept of "natural"-ness. Further, your inclusion of homosexuality made me think the underlying purpose of your post was to discredit the commonly made argument, "xxx is wrong because it is unnatural". (A la, "You can't say it's unnatural because it's hard to determine what is/isn't natural.)

But your responses to others make me think that maybe you're just trolling. So don't worry about it.

It seems pretty easy to determine what is natural.

Does it occur in nature? If so, then it is natural. The definition of "natural" does not make an appeal to religion, so there is no need to use any theological reasoning. 

Generally when people do use this word in a religious context, they mean "natural" to mean either "the way I think God intended it" or "occurs with great frequency".

Some people use words inaccurately. When you don't correct this usage, you allow them to confuse the issue, which can render the conversation pointless. Case in point: You clearly don't like that religious people use the word "unnatural" to condemn things they don't like. But instead of pointing out that they are misapplying the word "natural", you've gone and argued that the concept of "being natural" is some complex thing. In reality, it is not, and the issue has been confused. 

You've misapplied two logical rules.

First, a conditional statement is not logically equivalent to its inverse. 

Consider the claim, "It rained, so my grass is wet." Suppose it is true. The inverse is, "It did not rain, so my grass is not wet." This is not necessarily true, since the sprinkler could have gone off. You may be looking for the contrapositive.

Second, you are not correctly "distributing" the negation throughout the OR statement. That is,

~(A OR B) == ~A AND ~B. 

To see why this is true, let A be "it is raining" and B be "it is summer". If we have (A OR B) we are claiming that it is either raining or it is summer (or both). If we have ~(A OR B) we are claiming that is not the case that it is raining or it is summer. That is, we are claiming that it is not raining AND it is not summer. 

To summarize:

A → B is not equivalent to ~A → ~B. [inverse]

A → B is equivalent to ~B → ~A. [contrapositive]

~(A OR B) == (~A AND ~B) [De Morgan's Law]

To your point, the following would be a correct logical sequence:

P(x) → (∃xP(x) ∨ ¬∃xP(x))

¬(∃xP(x) ∨ ¬∃xP(x)) → ¬P(x)

(¬∃xP(x) ∧ ∃xP(x)) → ¬P(x)

The final statement is vacuously true, since its antecedent is apparently always false. (And any conditional with a false antecedent is defined to be true.)

I will give a concrete example. 

I dislike it when people litter, to a significant degree. When I see a friend litter, I want to tell them that they shouldn't litter. But when you use words like should and shouldn't, you're usually making an appeal to morality and this is where the trouble starts. 

In my worldview, there are no absolute moral rules. Littering is neither objectively right or wrong -- it simply doesn't have an absolute moral designation. Thus, I find it very difficult to tell someone they shouldn't litter because I don't actually believe that they shouldn't in an objective sense. I may not personally like it, but I find it hard to actually utter the words, "It is wrong," because I think that's a lie.

I don't know how to have conversations on moral issues without feeling hypocritical. I can talk about the pragmatics of littering all day long, but whether something is or isn't pragmatic does not suddenly give it moral value.

Littering irritates me, but I'm not doing the world much of a disservice by not saying it's wrong. The real problem comes with more touchy issues. I despise racism, but how can I say that racists are "wrong"? People who murder, people who prey upon the weakness of others, bigots, those with vile prejudice -- all of these people feel like scum to me. But how can I look any of these people in the eye and say they are objectively bad people when I don't believe things are objectively bad?

This is my problem. I don't know how to have a meaningful conversation about these issues if I can't even claim that there is someone who is absolutely in the wrong.

I hope that clarifies things a little bit, the issue I'm having is more difficult to put into words than I initially thought.

For the sake of this discussion, suppose you are a moral relativist. That is, suppose you don't believe that any moral laws, known or unknown, are true, correct, objective, or whatever label you prefer. 

With that in mind, I've had some trouble recently reconciling my moral relativism with my ability to discuss moral issues with other people. I have a personal moral code that I try to live by, but I fully believe that it entirely subjective and no more "correct" than anyone else's. I frequently hear other people talking about moral issues and their views on them, and I often find that I disagree with them. I want to have a conversation with them about it but I don't know how to properly do it.

How is one supposed to have a meaningful discussion about right and wrong with someone else if you fundamentally don't believe right and wrong objectively exist? It feels like I am essentially saying, "You should believe in my moral rules because I want you to." One can make these arguments from a pragmatic or compassionate or whatever standpoint, but valuing those standpoints still seems entirely arbitrary. 

Has anyone else struggled with this issue or otherwise see a way of dealing with it? I enjoy having moral discussions with others, but I don't like feeling like some sort of hypocrite or fraud.