He's pointing out that we have empirical evidence for the harm of certain substances and it's a different kind of harm than the largely unintended consequences of, say, cars, which provide us with far more direct advantages at reasonably low risk. The risk is also intentional and, to a degree, controllable with wild animals and intoxicated drivers being some of the major exceptions. (Inclement weather is at least partially controllable, as long as "don't drive" is a choice.)
But we also do have empirical evidence for the harm from cars. Thats what your parent is saying. The scale of harm is very minuscle when compared to car accidents. Even wars are less deadly than cars when just looking at the numbers. The reason you think intoxicated drivers are exceptions or that accidents are unintended consequences is that, in peoples minds accidents cause less emotions than the image of a poor baby with cockroaches with parents on drugs.
