There are two main reasons to cook wild mushrooms rather than serving them up raw. Raw wild mushrooms can be tough to digest, so cooking helps you avoid gastrointestinal distress, but also many are actually toxic and potentially deadly when raw. Cooking breaks down the harmful compounds, leaving you with a bowlful of mushroomy goodness [source: Michigan Mushroom Hunters Club].
While many raw foods can be hard to digest, wild mushrooms are especially difficult. Mushrooms' cell walls are different from the cell walls of fruits and veggies, and cooking breaks those down, so our bodies can handle processing the tough fungal cells. Breaking down those cell walls with cooking also helps you get more of their nutritional value [source: Campbell].
One caveat: There are a very few wild mushrooms that you can eat raw, but you'd better be an expert in identifying them. Mycologist David Campbell says that you can eat witch's butters and toothed jellies raw. He also describes eating a raw wild mushroom called the coccoli, which he marinates in lemon juice to make a mushroom ceviche [source: Campbell].
Different wild mushrooms need to be cooked differently. Some toxins break down when you expose them to heat. Others need to be boiled away [source: Campbell]. Campbell's lemon marinade is actually a sort of "chemical cooking" that works on certain mushrooms, but not others. Your best bet with wild mushrooms is to do your research to make sure that you cook them safely, and only buy wild mushrooms from trusted, reliable purveyors. It's literally a life-and-death issue.