I know from personal experience how crushing guilt can be. For most of my life I was my own worst critic, picking apart everything I did to find out what I did wrong, always assuming there was something that I missed, and usually not being disappointed. Recently, I became aware of the global devastation caused by participation in an economy that does not account for its impact on lives and ecosystems, and that awareness drove me to seriously consider the possibility that the world might be better off if I was dead. Only briefly did I think of suicide; but I'm not by nature a coward, and I chose instead the responsible option of justifying the rest of my life by trying to fix the damage and minimize future damage.
Part of my legacy of guilt comes from a Catholic upbringing, which should not be much of a surprise to anyone familiar with the Church. One of the attractions of Catholicism, and to a large extent other Christian denominations, is the promise of absolution of that guilt by the relatively easy commitment of one's life to the teachings of the organization. There is also the implicit assumption that an omnipotent deity can – and will – fix the big mistakes we make as long as we remain faithful to it. Absolution results in a brief state of spiritual purity (or at least, psychological comfort), which if we're diligent or just plain lucky, will follow us into an afterlife that is also devoid of need or want. In many of the organizations, the teachings we must accept include the literal interpretation of an ancient oral and written tradition that was formed before scientific enquiry led to an accurate and coherent picture of how even our little part of the Universe works. Members of these organizations are thus forced to choose between open-minded enquiry about the world and the package deal of emotional security and the promise of immortality.
The source of my remaining guilt followed me after I jettisoned my religious training and decided that as imperfect as we are, we're all we've got. This guilt was empirical, and was gradually reshaped by a new value system I began developing in the wake of my father's death. That value system currently promotes the maximizing of survival and evolution of Earth-based life in the Universe over the longest possible timeframe. If I took an action and could identify its impact in terms of my values, I could determine whether it was right or wrong and adjust future behavior accordingly.
Of course, in daily life, it's typically hard to make assessments of right and wrong in a timely manner (doing nothing, and not acting quick enough, have their own consequences). Dealing with this problem is the proper role for rules and laws, because they speed up the decision process. The downside of using these tools is that they must be periodically reviewed for relevancy and tested for usefulness (making sure they achieve the desired outcomes) in light of changing conditions and people.
Part of my flawed behavior, I realize, is that I continue to rely on other people's rules without adequately testing them first. I also need to develop new rules, which are grounded in a clear understanding of the variables affecting life's future. Finding and fixing the problems I've caused, and reducing what I continue to cause, to some extent depend on these prerequisites.
Absolution within this new moral frame of reference therefore comes from forgiveness for my ignorance and a dedication to doing better in the future. I would argue that this is the only truly effective definition anyone can apply.