You kill me!

Today was fungus foray day. We walked - about thirty of us - through mixed woodland, mostly birch and beech, and gathered about 60 species. I realised some important truths about fungus foraying. First, fungi are a long way down. Second, they are hard to see. Thirdly, the only sensible way to collect fungi is to take an army of youngsters with you: they are closer to the ground, they have 20-20 vision and they are very flexible.
And, of course, the thing that I already knew about fungi is that it's damned hard to remember their names, scientific or vernacular.
It was a great afternoon, in glorious autumn sunshine. I was left with one unresolved question. The deadliest of our native fungi is the "Death Cap", Amanita phalloides, which kills human beings in a very nasty way, but can be eaten by other mammals and by insects with no ill effects. My question is this: what does the Death Cap get out of killing human beings?