2 - marijuana is a more common first "drug" than hallucinogens, for good reason. Although temporary psychotic breaks CAN happen, they are rare, and it is an otherwise pretty innocuous drug.
3- as for hallucinogens: SET, SETTING, and DOSAGE.
Negative story: taking mushrooms with a friend when neither of us were in a good place, emotionally. [bad set] Got confused at the typical 20 minutes in when you "think nothing is happening maybe they didn't work" (this thought ALWAYS occurs) both ate more mushrooms. [bad dosage] Bad bad negative hallucinations. Head on upside down. Turned in to prehistoric bird. Friend outside on the street screaming racist epithets (not normally a racist dude) Luckily ghetto neighbors did not execute him (people can be much more tolerant than we give them credit for) police came and were astonishingly restrained, brought him to hospital. Very close call.
I still concur that hallucinogens are a great thing. But it bears repeating, respect Leary's SET, SETTING, and DOSAGE.