When the weather is nicer and we have more daylight, I frequently shoot at a public range. I haven't had to do it often, but several times I've had to speak up to keep people from doing something stupid. Only one time have I felt the shooter was being unsafe enough to really get in his face. I told him about the rules and when he was belligerent I suggested that we contact the park police for an interpretation of the rules.
I had my cell phone, and when I began the call, he packed up & left. This was a couple of years ago and I haven't seen him since.
Most times if you approach people in a non-threatening way, they quickly quit doing whatever stupid thing that they were doing. I've made a couple of long term friends this way.
To keep these public ranges open, we have to speak up. As soon as someone is injured and sues the park, the range will likely be closed.