It boils down to this:
Either one believes in right and wrong, or they dont. The question is, where did the notion of right and wrong come from? Is right and wrong subjective, or is there at least SOME form of standard to bear?
Let me explain. Many moral relativists argue that right and wrong are subjective, and are personally interpreted, and only through social agreement does something "become" moral or immoral. Let me address "social agreement". By our very nature as human beings, we agree with truth, and reject lies. When something is "true", humans tend to agree with it by our very nature. When something is "false", we tend to reject it. So, truth is an example of a standard, not a subjective observation.
2+2 is 4. That is a truth, and virtually everyone agrees. Therefore, 2+2=4 is not subjective, it's a truth, it's a standard. If some other person came along proclaiming "nope, 2+2 is actually 3", people would reject that interpretation as false.
SSM is not as tangible and rational as math though, but morality is. In order to come to a place of accepting this, a person must first acknowledge two truths, 1. Morality exists, and 2. No human being is responsible for creating it. These are BOTH truths. I challenge anyone to prove them wrong. Name me the person who created right and wrong. Can't be done. They just "are" right or wrong. But the notion had to be created somewhere, somehow, and by someone or something. This proves that morality is judged by a standard, not an individuals subjective interpretation, or the agreement of society.
A secular example is slavery. At one point in history, the majority of THIS NATION agreed that slavery was morally right, but it wasn't. Over time, society recognized that slavery was in fact IMMORAL, and worked to correct it. Did society's recognition change slavery from once being moral to being immoral? NO!!! Slavery was ALWAYS immoral. Man's recognition, or lack of recognition, of moral truth is irrellevant. Morality is weighed by a standard over all the ages.
Where did morality come from? Not man. The founding fathers of THIS NATION may not have all been "Christians", but they were classically educated men, and they all understood the two truths I mentioned earlier; 1. That morality exists, and 2. No human being is responsible for creating it. They recognized that certain "moral" truths were given to ALL of mankind. The right to life, liberty, and the pursuit of happiness. All have secular aspects, and all have moral aspects as well. They understood this. People today do not.