If you throw 100M people at this as a solution, do you expect to see most carefully and successfully getting through it like you or would most just become addicted and eventually lose their job and go homeless?
For small doses of psilocybin, it is - both in my experiences and in a lot of scientific contexts - considered very, very safe. Greater doses, 2.5 dry grams, you start to introduce risk triggering latent psycho-affective disorders.
For most people with common neurotic conditions, anxiety, depression, etc, it is very low risk. Out of 100M, I'd say .1% is at risk having a very negative experience due to significant, untreated issues like schizophrenia.
All of things things require support. Community, a guiding hand, will truly improve the outcome.
I can't say the same for alcohol, cocaine, and even cannabis. I know people who have had problems with all of them.