Initially I thought that manners are offshoots of morals. That manners and etiquette are byproducts of morals. Therefore they serve the same purpose as morals, albeit on a less grievous or serious tone. Both are needed for the smooth running of society.
However, I'm beginning to doubt if that's true. That manners and morals are related, is true. But does being well-mannered mean one is morally sound too - or the vice-versa. If one has his morals right, would he or she be well-mannered automatically? I don't think so.
One could be well behaved and polite and courteous in society, but in reality be an immoral person. Take for instance, the politician (one can practically include every politician, anywhere in the world). On the other hand, take a tribal or one belonging to the indigenous population. Or even a simple person from a rural setting. Most often they have their morality or ethical practices very sound. They are not really corrupted by the malicious mind of civilization and technology. However, his 'manners' may appear crude or unpolished.
From another viewpoint, would it be right to call someone who goes about swearing (not at anyone in particular, though) and behaving in an uncouth manner, immoral? Or would it be right to say that his moral compass is skewed? Manners are contextual while morals are universal (or are they?). Manners change as per place, time, persons, occasions. Morals don't (at least not as fluidly as manners).