One person with no symptoms can be shedding the virus and can exponentially infect hundreds of people. Every door handle, cup, plate, chair, bannister etc can be virus laden.
The people who are visiting and the hosts are being completely stupid. For some people a police interview or a monetary fine are the only way they can be made to understand. Having said that, I read about a young man whose fine has been trebled and he still wanders around town aimlessly.
We are in the Lakes, and several families have been caught trying to sneak into the area overnight! They needed a bit of a holiday apparently. Despite the fact that there are very few hospitals, huge distances apart, and pretty small! All the hotels, cafes, non food shops, attractions and car parks are closed. One family had travelled over 200 miles.
What were they thinking?