If a stranger threatens me on the street with a knife, and I pull a gun, I have to be very careful and have a clear plan. If I shoot and miss and hit a car behind the guy, I'm liable for the damages. If I shoot and kill the guy and the knife falls away somewhere and can't be found, self-defense isn't going to hold up. I have a lot to worry about other than the fact that someone is suddenly threatening my life.
If I see someone breaking into me car, I can't go tackle the guy. I have to hide in the shadows, call the police, and hope they get to the scene before he gets away. A police officer literally told me exactly this before.
It makes one question how much thier "protection" really protects us.
I was once shot at by someone sellling drugs in a neighborhood park. I ran and hid but not before I got the plates on his car. I immediately called the cops with the plates, year, make and model of the car. The cop informed me that none of that information would help. As far as I know, he did nothing.
We're not allowed by the law to take matters into our own hands. Law abiding citizens are suppose to tell their babysitters that something bad happened, and anyone who has dealt with the police know how incredibly rare it is for them to actually help out.
One more story. I was a victim of a hit and run on the freeway at 70 miles/hour. I chased the person while my wife in the passenger seat took pictures and recorded everything. I caught the person. It was someone with no license, no insurance, and didn't speak English. When the police arrived he informed me over and over that this was classified as an "accident". The person got a citation. They didn't inform us of the court date until after it happened.
Damned if you do, and damned if you don't in terms of taking matters into your own hands.