NPR has an article on the downside of mushroom foraging – the damage done by some mushroom hunters to the habitat such as state parks. This quote about what has happened at Salt Point State Park in California is a good example of the problem:
As a result, known mushroom grounds are taking a beating. At Salt Point State Park, mushroom hunters sometimes carve new trails into the forest, trample small plants, and illegally use rakes and shovels to turn over the forest floor in search of young, budding mushrooms, according to Farcau. Some, he adds, leave trash piles by the road and toilet paper in the woods.