Function of amatoxins

There are a couple of papers and "lots" of anectodal evidence which imply that mushroom hunting does not have any adverse effects on the fungi, neither short nor long term. One of the counter arguments for that is that some fungi developed deadly toxins and what reason do they have other than stoping animals from eating them?

So, I had this discussion recently and I raised this point. I was told that many compounds that fungi produce do nothing for the fungus and they are producing them just because they are not costly enough to be cut by evolution. I don’t find this argument particularly compelling, so I was wondering whether we know anything about the function of such compounds, say amatoxins.

Do they have any function other than killing us? Are they used by the fungus for anything during its life cycle? Do they kill insects or larvae? Do we know anything about them?