The box I cobbled together from old pallets, dirt is a mix of potting soil and local dirt spiced with chicken poo.
For the more observant viewers, you may notice that the closest 'V' is slimmer than the upper square -- the pallets were a little short. I plan to plant smaller vegetables in those areas.
I agree that it's a bit of fear mongering but it's for a garden that will be growing food for years. To use your analogy, the chance of being hit by a bus when crossing the street is tiny, but I still look both ways because of the tiny possibility that a vehicle is going to run a red light.