Ah, yes, that would be the infamous Blue Boy episode. The first part of the episode takes place before LSD was made illegal (in 1966), and so the only punishment the blue boy gets is being returned to his parents and a firm lecture from Joe. Later on in the episode, LSD has been made illegal and one of the blue boy’s friends overdoses on LSD (!) and dies. The part about “it’s not like it’s marijuana” is definitely Webb wagging his finger at society for taking so long to make LSD illegal.
(Some have noted the irony in this being the first Dragnet episode aired in color.)