Memes

Even some of the ones that are edible still secretly want to kill you. From the Wikipedia entry for "chicken of the woods":

In some cases eating the mushroom "causes mild reactions ... for example, "swollen lips" or in rare cases "nausea, vomiting, dizziness and disorientation" to those who are sensitive. This is believed to be due to a number of factors that include allergies to the mushroom's protein or toxins which are only somewhat stable at high temperatures.

I'll eat portabellos if they come on pasta or pizza (though I've started taking them off the latter because they turn to rubber in the microwave) but I sure as hell am not going out of my way to order any dish that features them (mushrooms) as the main protein.