Sin during the time period of The Scarlet Letter was defined by the Bible. Today sin is determined via both the Bible and society. Our society changes what is sinful and not based on the time period and the caliber of celebrity of the person. The consequences are the same in regards to the feelings elicited from the subject. The idea of punishment, shame and public outcry has not changed.
The idea of sin and the consequences are drastically different from the time period of the Scarlet Letter to today. Today, many people deny that sin even exists. In the Puritan era (the timeperiod of the Scarlet Letter) sin and the law were one and the same. The first few chapters of the novel talk about the ideas of Puritan law, sin, and punishment. If a child were disobedient in those times, the parents could hand them over to the magistrates to be publicly whipped. If a servant was lazy, they could also be handed over to the government. And obviously, adultery was a crime punishable by death. Today, sin in a lot of ways is a much more private issue. Consequences are also many times much more private. Parents deal with their own children, etc. Adultery is not considered worthy of the death penalty.
The time difference is great! The Salem Witch trials took place in the late 1600's, which is around the time frame that is set for the Scarlet Letter. Of course, legal punishment is no longer an issue for adulterers, but the moral stigma still exists.
While we certainly don't brand adulteresses with a scarlett "A" to make them identifiable to the public at large, and thankfully children born out of wedlock don't bear the humiliation of being known as a bastard (in most cases.) However, society still holds to a standard of motherhood that is pretty rigid. Many a working mother can attest to the pressure put on her to be more involved; parenting skills are constantly scrutinized...look at Britney Spears, for example. While I do not exclude myself from those who would call her a "bad" mother, the truth is that it is no business of mine. Still, we penalize or reward those who are christened good or bad, sinful or virtuous.