I don't disagree, but I think you overestimate the ability of people to be careful and aware of their surroundings at all times. Or to even remember that it's an issue. Magnetic fields are invisible. A pacemaker patient I know was unaware of the (potential and low) risk posed by induction hobs. I'm sure this was explained to him, but not everyone is a pacemaker (or magnetic field) expert, nor can we expect everyone to be.