"Why can't it be about your health?" Dirk's question is mostly rhetorical, though he does find the inference that he wouldn't be concerned about that to be mildly offensive.

"In a way, it is. The repeated consumption of psychoactive substances to alter your brain chemistry is a bad pattern to fall into. Once you make a habit of it, you've made yourself a problem that's just not worth the illusion of its temporary benefits."