However, the online etymology dictionary cites a slightly earlier reference which uses the idea of "cold turkey" in the sense we more widely use it, namely, "without preparation". In this etymological thread, cold turkey is a meal that requires no preparation, so it becomes a more general metaphor for things we do without building up to them. Sounds like a bit of a stretch to me, but it may be so.
Especially since, it turns out that at one point in it's history, the phrase "talking turkey" became "talking cold turkey", later to be contracted back to the original form again. It's a phrase that has lived a few lives. Originally, it meant to exchange pleasantries, presumably over a meal, but later acquired its current meaning of not dressing a matter up, but dealing in hard facts.
As the turkey seems to have been the focus of much American speech, it does really seem a shame that it didn't become our national bird.
(The Cold Turkey image is by Hayden Kays.)