system
Given the following post, respond as if you're commenting on Reddit:
human
Why is it that a single good deed isn’t enough to pardon a life of evilness but a single act of evil is enough to condemn a life of good deeds?

This was a quote in a movie. But this seems to be true in real life as well.

By extension, if we quantify good vs evil, does this imply effect of 1 unit of good < effect 1 unit of evil?

And depending on the answer, do utilitarians take this factor into consideration?  That, for example, harming 1 person may irrespectively outweigh the good caused to the other four because of the above fact?
gpt
From the point of view of moral psychology, it's to do with trust.

Our conceptions of morality and especially our moral intuitions serve to structure our social interactions. When we think about people being good or evil, that informs our interactions with them. We don't just enter into every social interaction with a blank-slate absence of expectations. We form opinions of people, gossip, share information, and create reputations, all to inform us what to expect when dealing with one another, and how to treat each other. If someone is a war criminal, we want to *know* that before going for coffee with them. 

Now, 'good' and 'evil' aren't just value-neutral valences on a scale, like +1 and -1; they're qualitatively distinct. When someone not only fails to do good but acts in a way that can be described as evil, this *undermines* much of the credit we might otherwise give them for the good they've done.

As other commenters have suggested, the more general psychological phenomenon of negativity bias might also be a factor. We're more alert and sensitive to threats than we are to the positive counterparts of negative stimuli or experiences, because evolutionarily speaking, the cost of missing a warning sign can be a lot higher than missing something potentially good. Applied to people's characters, it's safer to err on the side of condemning evil.

This only works up to a point, though, namely so far as to not make trust and cooperation impossible. If everyone is *too* quick to condemn each other, let alone enact revenge, social cooperation collapses. I'd say that's why the quote is a bit overly simplified. There is an asymmetry there, but it's not fully one-sided.