"Manners are of more importance than laws." claimed Edmund Burke, "According to their quality, they aid morals, or they destroy them." Be that as it may, such sentiments mean nothing to ... The Thing That Wouldn't Leave!
Why bother with good manners, especially given the times we live in? Well, as journalist Henry Hazlitt once noted, “Manners are to morals as the final sand papering, rubbing, and polishing on a fine piece of furniture are to the selection of the wood, the sawing, chiseling, and fitting. They are the finishing touch.” Basically, good manners point to something deeper in a person's character.
And what would that be? Virtue. Temperance and charity are the respective cardinal and theological virtues which form the basis for good manners. Temperance ensures the will's mastery over instincts and keeps desires within the limits of what is honorable; charity ensures we love our neighbors as ourselves. So, in theory, good manners show your willingness to keep your reactions in check out of charitable love for others. In theory. Of course, you can fake manners like anything else. But if that's the case, that opints to something deeper as well, doesn't it?