You are not above reproach. You are not infallible. You can one day find yourself at the receiving end of a justice system that you helped to create that will not take into account your special circumstances.
The reason why we have "innocent until proven guilty" as our standard (and why it doesn't always apply to social settings) is because our forefathers knew that even a just system would necessarily be flawed because people are the creators, and so it was therefore more acceptable to err on the side of leniency where some criminals might go free than on the side of harshness where innocent people might be punished. Our current system, even *with* that aphorism supposedly guiding it, has swung too far to the wrong side. And then there's the middle ground where one's innocence or guilt is not in question, but they are nevertheless fully nuanced humans because no one is a cardboard cutout, comic book, black-hat villain.
You cannot see yourself ever being in one of these unfortunate positions because you have convinced yourself that you are a Good Person, and Good People do not do Bad Things. Those people did Bad Things, therefore they are Bad People. You are the problem. You are the reason why people do Bad Things and why people continue to do Bad Things. Everyone thinks that they are morally and ethically right in what they do, because everyone thinks that they are Good People. That kind of thinking is what blinds people to the fact that they fucked up and did something bad. That kind of thinking is what prevents people from learning empathy or from taking responsibility and holding themselves accountable for their actions.
The knowledge that there is no understanding, no forgiveness, no second chances, no contextual exemptions or explanations, no space to repent and do better, is what drives people who do Bad Things underground and what drives them to continue doing them. Why should anyone feel bad about their mistakes? Why should anyone stop making their mistakes? Why should they ask for help in ceasing their mistakes if there is no room for them, if there is no safe space for them to change? They are lost souls. They are cast-outs. They are doomed. So why bother to fix anything? Their situation is your doing.
And you may one day find yourself on the receiving end of your "justice" precisely because you cannot conceive of being in that position so you will be unable to predict or prevent the thoughts that lead to the actions that carry you to that position.
YOU ARE PART OF THE PROBLEM.
There is a very big difference between drawing strong boundaries around ourselves and how we relate to, interact with, or feel about someone who has done Bad Things personally, and giving the government the power to make irrevocable punishments and decisions over people who do Bad Things. While we absolutely need a system of justice to deal with people who do Bad Things and while we absolutely can draw whatever personal boundaries we want regarding other people, setting the same consequences for both personal feelings and the government penal system is very dangerous.
That led to witch burnings and lynchings and a for-profit prison system that punishes black pot smokers because of *personal* feelings towards those kinds of behaviours. The reason for leniency in the penal system is because, at any moment, we could find ourselves on the receiving end of an unjust system with an enormous amount of power. All it takes is either the system being controlled by people who have different value systems from ours, or one of those complicated, nuanced situations popping up where we are able to rationalize how "it's different when I do it".
Look at the no-tolerance laws for drugs and weapons on school campuses! People who can't see themselves in that situation or who think of themselves as Good People don't see how it was inevitable that the law would eventually start penalizing children for their asthma medication or bringing in their homemade clocks to show their teachers. Part of that is because of the Good Person fallacy that they're committing and part of that is because they are part of a privileged demographic who is not likely to be unfairly targeted by ridiculous interpretations of those rules.
We all do shit that other people think is unforgivable or heinous. Most of the time, we feel justified in having done those things, which is why we did them. Those no-tolerance attitudes can be applied back on us. Other times, we might have genuinely learned from our mistakes and grown as people. Had the penalty for our crimes been death, we would not have become the productive members of society that we are now, with people who love us and accomplishments and acts of redemption. Had the penalty been death and we just never got caught, we would be unlikely to have sought help to find accountability or even changed our outlook to one in which we now admit our wrongdoing, because to do so would have meant our death.
Had the penalties been other atrocities like rape or castration or assault, even though we might have lived through it, those things would have damaged us which decreases the chances that we could have found redemption, accepted accountability, or learned empathy or regret. Those penalties would likely have exacerbated the problem. Those penalties would likely have made us worse or more broken people instead of given us a chance to get better.