Social Law vs. Moral Law

So why does society so often dictate what is morally right? Is not moral law firmly set and unchanging from society to society? Why are people perceived as being morally wrong because of something they do that is only socially wrong?

Examples:

In America's Bible Belt a 22 year old Christian enjoys alcoholic beverages. He does so liberally, but legally and responsibly, staying in complete control. Now it is not hard to imagine that in this society there would be more than just a handful of people frowning upon his/her behavior and making a judgment on his/her morality.
In Germany, they same person does the same thing. Would anyone question this person's morality in this society?

In some circles, one must be very careful of using certain words deemed profanity, else be viewed as talking in an immoral way.
In other circles, the words that fall into the "immoral" profanity category tend to be different.

Is it immoral to drink a beer? No. Is it immoral to use profanity? No.
And yet depending on the society one is in, a person associated with these behaviors could very easily be dubbed immoral because of certain actions like these.

And so I ask again, how has society gotten the upperhand that dictates morality?

Let morals dictate society's laws; not the other way around.