If we could count on unsafe drivers getting tickets, then maybe that would be acceptable, but that's not how it works. It's really hard to quantity "safety". It's really easy to quantity speed. It's difficult to quantify what speed is safe, so in most cases, we pick an arbitrary number, which damn near everyone ignores. At least where I live, 5 over is a minimum, 10-15 over is common. So cops can pretty much pull anyone over at a whim. And they do. But they don't make a dent in actual unsafe driving.