On some level, it feels like (some) politicians haven't realised this, or have forgotten it.

We can either have a functioning democracy and justice system, where responsibility is delegated to people whose job it is to uphold society's values, or we can have individual people that do job themselves. If a judge or police officer isn't going to carry out justice, then eventually people are going to do it themselves. That tends to get messy, so we stopped doing that with good reason, and built institutions to better service justice, but if the institutions aren't doing their jobs, they should be reformed or thrown out.