Until you run into an A-hole whose response ruins the rest of your day when you were just trying to be sociable. I could even see getting physically assaulted for trying to talk to the wrong stranger. I like where your heart is at, unfortunately many people out there are not deserving of it.
The idea of practicing these random interactions is also to get accustomed to rejections from the assholes. After all, they aren’t the majority- most people are actually quite nice and often appreciate a company (or will politely tell you they don’t need one)