We know that past a certain point harsher punishments in general are not a deterrent to people committing crimes so we need the public to grow a spine and reject the idea of excessive sentences since while it makes them feel safe, it's just putting them at further risk. Some facts are a hard sell to people though, especially when they're afraid.
We have a huge problem with mass incarceration in the US and the treatment of people we lock up and the conditions of those facilities need major reform, but I don't think we should abandon the idea of locking people up as a punishment entirely.