"The reason we are against racism is because a person's race is sacred. A person's ethnicity is sacred. You cannot violate it. My race is sacred; your race is sacred; I dare not violate it. The reason we react against the issue of homosexuality the way we do is because sexuality is sacred. You cannot violate it. How do you treat one as sacred and desacrelize the other? Sex is a sacred gift of God. I can no longer justify an aberration of it in somebody else's life than I can justify my own proclivities to go beyond my marital boundaries.
Every man here who is an able-bodied man will tell you temptation stalks you every day. Does it have anything to do with your love for your spouse? Probably not, because you can love your spouse with 100% desire to love the person, but the human body reacts to the sight entertained by the imagination and gives you all kinds of false hints that stolen waters are going to be sweeter. They are not. They leave you emptier. So a disposition or a proclivity does not justify expressing that disposition and that proclivity. That goes across the board for all sexuality.
When God created mankind and womankind, it was His plan, not our plan. It is extraordinary what He said. He said, 'It is not good for man to live alone.' Well, man wasn't living alone; God was with him. Why did He say that? He created the mystique and the majesty and the charm and the complimentary nature of womankind in a way that made it possible for her to meet his emotional needs that God, Himself, put only within her outside himself from himself in her in that complimentariness. It is a design by God." -Ravi Zacharias*
The Value of Race and Sexuality
Something that I want to point out: if God does not exist, race is not sacred, and neither is sexuality- there is no intrinsic value in either if God does not exist. If there is no value to be violated, there cannot be a violation. If God does not exist, anyone who stands against homosexuality is just as justified as anyone who promotes it, because a violation cannot occur on either side.
The problem, though, for the atheist comes when we realize that on that worldview, race also has no intrinsic value. If there is no value to be violated, there cannot be a violation. The person who promotes racial diversity is just as justified as the person who wishes to stifle it or even subjugate other races. Violation of a value cannot occur on either side if that value does not actually exist. (For more on this see "Martin Luther King Jr. vs. Evolution")
Morality Without God
If we are to believe that what is "good" or "right" is determined by the individual, then racism, sexism, homophobia, and any other behavior can be said to be "good" and "right" by any individual. And another individual cannot say that that person is "bad" or "wrong" without appealing to their own individual morality. The result is a stalemate, until one overcomes the other ("might makes right"). This is called subjectivism.
If we are to believe that what is "good" or "right" is determined by a culture or society (called relativism), we must remember that cultures and societies are made of individuals. However, this does add another interesting layer to the subjectivism described above. If the culture or society determines was is right, then there is no "right" way to change the culture or society. Anyone who speaks against the culture or society is committing a violation of that society's morals. The implications of this are that the stand against racism was wrong and the current stand against "homophobia" and traditional marriage is wrong. You cannot have both without being inconsistent (not that consistency has any "right" or "wrong" value in an atheistic worldview either).
"Thriving of a species"
Another philosophy of morality that has become popular in atheistic circle is the idea that morality of an action or behavior should be based whether it promotes the thriving of a species. Any action or behavior that does so is considered "good" and "right". This can and does allow one to stand against racism; however, it does not allow one to stand against homosexuality. Homosexuality actually prevents the thriving of a species. If all members of the species were homosexual, the species would become extinct within a few generations (accidents of confusion are bound to occur, if you know what I mean). Even with some confused homosexual individuals, the population of the species would dwindle to extinction. Thriving is the complete opposite of extinction, and any behavior that would lead that way is wrong and bad on this view. Anyone who stands against a behavior that leads to extinction of a species is promoting the thriving of that species. Therefore anyone who stands against homosexuality is right, and anyone who support is wrong, on this view.
On atheism, regardless of which moral philosophy you subscribe to, there are consequences that you will have to live with. However, if you deem those consequences "wrong", then you have just affirmed subjectivism, and you had better be prepared to argue and fight for your subjective view of morality, because others will be ready to argue and fight for theirs. However, if you believe that fighting is wrong, then you must face the reality that your combination of views will be removed from the scene. The only way for a view to survive the test of time (if atheism is true) is to have a violent adherent.
Responding to Critique
Before I delve into the benefits and consquences of morality based on God, I want to point out something that many atheists are bound to latch onto about my above critiques: they ALL make an appeal to emotion. The emotional force of those arguments come from the fact that we understand that there is something intrinsically "wrong" with the implications of those views. That understanding and uncomfortableness leads us to conclude to that they must incorrectly describe reality.
If one wishes to dismiss my argument as false appeals to emotion (a fallacy in logic), they must be able to demonstrate that the emotional reaction is not due to its accurate reflection of reality. If an emotion rises because it accurately reflects reality, then it is a perfectly valid appeal. One would then need to critique my reasoning based on intrinsic laws of logic (established apart from human intuition AND the universe; otherwise, we have another subjective or relative foundation by which we are "reasoning", both of which fall by the same critiques as moral subjectivism and moral relativism given above). But if one wishes to fight for logical subjectivism or logical relativism, then one cannot objectively say that my appeals to emotion are actually fallacies in actual logic to begin with. So, why fight? (Can We Be Good Without God?)
Morality With God
When morality is grounded in an eternal Being and not in an individual or culture, everyone has a foundation for saying that an action or behavior is definitely "right" or definitely "wrong". The problem is that many people don't like this idea. As described by Dr. Zacharias in the quote above, we have many desires that pull us towards actions and behaviors that are wrong, but those desires do not make the wrong to be right. What is right and what is wrong are not grounded in personal feelings, whether or not the source of those feelings are volitional or genetic.
If morality is grounded in anything but an eternal Being, then one must fight, to see their views continue, until either they give up of their own free will, or nature forces them to give up (by health or death). Since no two people will hold the exact same values, there is no guarantee that a person's values will continue even after they die. One may believe that they have fought for a "good" cause, but that "good" cause is not going to last for long. Looking forward, the atheist who fights for any "moral" position must ask themselves, "Why am I wasting my energy? What is the ultimate purpose of such a fight?" and understand that there will never be an answer, because one does not exist, though they desire for the answer to exist and be made known to them. Yes, this is another appeal to emotions, but I refer you to my discussion above about emotional appeals.
On the other hand, the theist may ask that question and can answer it twofold: what they are fighting for IS right or IS wrong; because of those objective facts of reality, the purpose of their fight is objective, and ultimately the purpose of their life is objective. This desire to know that the morality we stand for is good, and that the fight is purposeful is fulfilled if and only if God exists. Even though we must fight for what is true, the success of such a fight does not depend necessarily on us as individuals. Because of that, and knowing that God exists and is the source of morality satisfies a great human desire and frees the Christian to fight calmly and when called upon, without feeling that if they don't fight hard enough or long enough or dirty enough, the cause will be lost.
Consequences and Conclusion
The primary moral consequence of a theistic world is that we will have to give up acting on some desires and proclivities. We will have to tell our friends and family that certain actions and/or behaviors they participate in are objectively wrong. But how they react to the truth is up to them, no person can change the heart of someone bent on acting against God (another burden freed from the Christian that must be carried by the atheist). How a person reacts to the truth reveals who they are, not how well the deliverer of the news delivered it. It is the responsibility of the receiver, which receivers of moral news do not like to hear- emotions run high in defense of their behavior (above, on emotions again)- rationalizations begin to be developed and communicated with ever-increasing fervour- the futile fight for moral subjectivity now consumes the sinful individual. When(If) they realize the futility, only a recognition of and surrender to God will help them realize the value of their existence and satisfy the desire they tried to fulfill with what they thought would bring them pleasure. It is only at the Cross of Jesus Christ that man's deepest desires are satisfied permanently. God loved us so much that he died so that we might live a life with fulfillment, forgiveness, purpose, and hope.
More On The Topic of Homosexuality:
Legalizing Morality: Is It Wise, Is It Legal, Is It Possible?
Christian Ethics: Issues and Options
*From this week's Q&A edition of the podcast Just Thinking.