Take seatbelts - the oft-given example - if I don't buckle up I might die in a crash but it doesn't harm anyone else.
Incorrect. You are now a 180Lbs loose object in the car. Where your children were safely buckled, your dead body bounced to the back seat and injured them. Or you're a 450Lbs object wedged behind the steering wheel... This is slashdot after all.
Seeing as we were talking about the UK we can also talk about the fact that increased injuries of loose drivers/passengers if they don't manage to die will affect others by the increased cost and use of resources in the NHS.