Most people have felt guilty at some point of time in their lives. Guilt is about looking back at past events with remorse - when they realise that they "should" or "could" have acted differently. Sometimes, the feeling of remorse is based on inputs that are given by others, and not by self-realisation - this is when the thoughts that is imposed is that they "should" have acted differently. When this remorse comes from self-realisation, then the feeling is that they "could" have acted differently. At the surface both forms of guilt and remorse appear the same, and upon further thinking, it will become apparent that they are two different things altogether. When it comes from self-realisation and acceptance, inbuilt in guilt and remorse is the concept of "choice." When it is imposed by others, then sometimes, it turns out to be emotional manipulation.
Guilt is useful in the sense that it helps keep us focused and do the best we can. Like fear, guilt also helps in keeping us grounded and acting appropriately as possible. However, the condition is that one can only do what they truly believe to be "good" and useful. In that sense, there is a fine line between innocence and ignorance. (For more on Innocence Vs. Ignorance)
What is Guilt? Synonyms for the word includes culpability, guiltiness, blame, blameworthiness, wrongdoing, wrong, wrongfulness, criminality, unlawfulness, misconduct, delinquency, sin, sinfulness, iniquity, etc.
Guilt is a learned social emotion that has major psychological and behavioural components and outcomes. Guilt comes from social and cultural programming, which begins from childhood. It is also built into our legal and social framework so much that it is almost impossible to consider life without it. The legal system uses the word “guilty” or “not guilty.” The meaning of the word is given as “the fact of having committed a specified or implied offence or crime.”
The key is that like with all social emotions and norms, it has to do with the prevailing thinking at any slice in time - for example, what was absolutely alright 100 years ago, is not any more. History is replete with such instances. So, any evaluation or judgment is based on the prevailing social constructs. Remember: there was a point in time that society allowed advertising smoking of cigarettes as fashionable and even medically useful! And documented history as late as 150 years ago, shows that humans were enslaved and traded like commodities and livestock!
There are some norms for expected behaviour that have been around for far longer. And in these cases the programming starts in childhood, and is often done by well-meaning people who probably do not know how else to inspire the children and to teach them appropriate behaviours. And since guilt brings about a negative feeling it helps obtain a quicker response - hence may seem more useful for short term results. The long term ill-effects of using such