In making 40k analogies, it's best to stay away from the more recent iterations of the lore, as in many ways 40k has become a third-rate fanfic of itself.
The only comparisons worth making are to the early (mid 80s to early 90s) stuff, when the nature of the Warp, the Chaos Gods and the God-Emperor of Mankind were first being laid down in print. My understanding is that Bakker was into D&D in a big way in the mid-late 80s, which means he was probably reading White Dwarf magazine, at least sporadically, just at the time that those aspects of the 40k lore were being excerpted there from the Realms of Chaos books.
Anyway, about the rats thing. Later experiments showed that rats only get hopelessly addicted if they're stressed to begin with (e.g. from being kept in a tiny fucking cage with no stimuli). Rats kept in an 'enriched' environment will still give themselves cocaine hits occasionally, but they don't show the classical addiction symptoms of just sitting there dosing themselves continuously to the exclusion of all else. Humans seem to show the same dichotomy. Poor, stressed, miserable folks get addicted really easily. As do rich but tormented types (e.g. celebrity introverts). But lots of affluent and not-particularly-stressed-out people do illegal drugs without any real ill-effects. They're not as newsworthy as the celeb overdose-suicides, and they don't usually come to the attentions of law-enforcement, of course, so you seldom hear about them.
