Since before there were cell phones, a subset of people have generally been rude and uncaring about their behavior in regards to those around them. As I now have an infant to care for, I am acutely aware of those around me and do not wish my child to disrupt anyone's dinner at the local sit down eatery, or wherever. There are people who don't care how loud their child screams and/or causes a scene, and this was the case before mobile phone were ubiquitous. I usually pick up the child and move him away from those enjoying their dinner or activity if there is a period of fussiness and/or noisiness. I treat my mobile as gingerly as a child, apologizing for any noise or disruption and excusing myself if something is pressing. However, the use of a jamming device is an even higher level of rudeness, and I see it as the equivalent of someone else attempting to discipline my child for me. Regardless of how poor I may be at it, it's still my responsibility. It's difficult to go around smacking everyone in this world that you may find rude or insulting without recourse. And there's still such a thing as asking someone politely to knock it off.