You're right -- the lethal dosage of cocaine is about 95 milligrams per kilogram of body weight. This translates to about 6.5 grams for a 150-lb person. [0]
You neglected to mention that the lethal dose for caffeine is in the same magnitude -- "150-200mg per kg of body weight, or 5 to 10 grams of total caffeine ingested, is considered lethal." [1]
Given that the street price of cocaine in the USA is around $120 / gram [2], it would cost about $780 to overdose. Meanwhile, I can easily and legally order 16 grams of caffeine tablets online (or in any CVS) [3] for $11.49 -- enough to kill two people.
Does this cause you to rethink any assumptions?
Don't forget -- at one time, drinking coffee in public was punishable by death. [4]