I'm reminded of the Far Side Cartoon where everyone decides to become a vegetarian, and through a reducto ad absurdem argument such as you are offering, end up hanging upside-down on tree branches because they don't want to step on bugs, either. The vegetarian rule is simple: don't eat anything which has eyes, parents, or screams when you kill it. I've heard a hundred variations on the silly "plants live off dead matter" argument; you're hardly original.
No, it wasn't that. Actually mushrooms and fungus do not belong to Kingdom Animal or Plantae. They are Kingdom Fungi, and they feed directly on dead materials.
Plants only feed on what the fungi leave behind in the ground.
What do vegetarians think about that ? Is it edible or not ? Especially considering that fungus is actually some of the most efficient lifeforms around as far as converting food to body mass metabolisms.