Back in Old Testament times, a follower of God who had sinned had a fairly organized rubric for what he needed to do in order to get 'back right with God'. Basically he had to sacrifice an assortment of animals through approved clergy and make restitution to whoever besides God that he had injured through his actions. Since there hasn't been a properly consecrated temple for a very very long time (AD 70ish), if you're still observing that covenant there exists a massive sin backlog.
If you're a Christian, you believe that God replaced that covenant with a new and improved version, where Jesus served as the sufficient and perfect sacrifice for all sins that were, are, or are yet to come. God still commanded, though, that Christians were to make restitution to those besides Him that they had injured, and to confess their sins to one another and thereby take the social status hits associated with such confession. A very very dim view of gossip was taken though, so in a functional Christian community this wouldn't have been quite as scary as it might sound to modern ears. The Catholic church later formalized this into the sacrament of confession, appealing to Jesus' grant of power to forgive or retain sins to Peter, upon whom he would build His Church. There, instead of confessing your sins in what might amount to a neighborhood prayer meeting, you instead confess to a priest who has lots of experience maintaining confidentiality and who has probably heard far worse than the tawdry sins you're confessing. I find this far less intimidating, as do most people, which is probably why the practice caught on so strongly.
Sometime later on, some brilliant theologian got the idea that the Saints had built up SO much 'good works capital' that lots of it could be sold in the form of indulgences (the Catholic church still grants indulgences, they just don't sell them anymore). Here, people with unresolved guilt could purchase indulgences, which would be used to fund the magnificent architectural and cultural contributions of the Church at the height of its temporal power. Of course this didn't last, it lead fairly predictably to the Reformation, and few Protestants today have anything remotely like either the free for all confession of the Early Church or the organized confession sacrament of the Catholics.
Interestingly enough, few Catholics these days go to confession either---the matter is considered scandalous. So there's all kinds of unresolved guilt that people have in modern America. And how do they resolve it?
Well, there's a new step in the evolution of indulgences. Instead of doing penance for one's sins, or paying for an indulgence for the same, we now, in our upper middle class SWPL segments, outsource the penance and payment for the indulgences instead to other groups that we don't like or who compete with us for status.
So, instead of giving to the poor, we lobby for income redistribution away from other groups. Instead of living simply so others could simply live, we lobby to force other people to live more simply. To expiate the perceived sins of racism, we lobby for Section 8 housing in OTHER people's neighborhoods, and for the discrimination in terms of allocation of society's goodies against OTHER people's children.
Frankly I think I prefer the medieval version---oh, how did it go? When the coin in the bottom of the coffer rings, the soul, from Purgatory springs? At least the sinners in question usually paid with their own money.