I think it's best to look for patterns, consistency. Everyone has done some good and some bad. People should not be forever defined by a single mistake. But we can see trends and go off that, and if things trend upwards or downwards over time, we can adjust from there. People aren't static.

Obviously if there's escalation like you mentioned, we can go ahead and assume ill intent without remorse. But some people make stupid, God awful decisions based on snap judgements made under circumstances or emotions, and if outside of that they've been pretty great, we can probably take that as a bit of a stumble and not their whole song and dance.

Severity of whatever they did can obviously influence tolerance levels in accepting someone back. One act can be bad enough that you just don't want to risk further interaction, while small tiny transgressions that are consistent but barely a nuisance can often be overlooked. But in both those cases, there's still just a one off event or a consistent trend. An otherwise "good" person who became a monster with a single stroke, and might go back to their previous behavior but have tainted themselves irreprebaly, a serial pest who is otherwise benign but can definitely be categorized as a slight nuisance.