It starts with cutting in line. When people are guilted into thinking "No big deal, it only happens once in a while", they are surprised to see the behavior propagate and subsequently ask "Why is everyone cutting in line now? What happened to manners?"

I think arguing for the appropriate punishment makes sense, but the "not a big deal" attitude is how society devolves. People didn't just spontaneously develop customs and norms. Certain pressures existed to create them.