It can seem 'easy' to distinguish when familiar. But if you're coming at it fresh it's quite daunting. And to make your friends sick is a significant faux pas.
Anyway that leaves the "I don't want to do this, and I want a 'good reason' and the death card is a good reason" cause of reluctance. It may be more common that we think.
Especially after I've picked something, it is really easy to move backwards and say "is there uncertainty with what this could be?".
If you are making educated identifications (which is really easy to do with the materials available in this age) you shouldn't ever be vomiting when eating mushrooms.
A very small percentage of people cannot handle most of the mushrooms that other people can and will vomit but this is true of many other food categories and is not unique to mushrooms.
We're talking the entire class of little to no culinary value little brown things. Name some tasty ones, go!
Now let's bring in the 'lets get fucked up' crowd and see how much chaos can happen.