What's the origin of the expression "to quit cold turkey"?

Answer 1

The above answer is right, but also, the phrase turkey comes from the drug addicts, especially heroin addicts, where the really bad withdrawal crisis causes uncontrollable muscle spasms of arms and legs which resemble flapping, and making uncontrollable guttural noises, like the gobble gobble.
The addicts break in cold sweat, sometimes with goose bumps, and are very pale.

Answer 2

Since "cold turkey" is normally used in the context of quitting an unhealthy habit, such as smoking the phrase describes the skin's reaction to heroin withdrawal. As an addict stops using the drug, blood is drawn toward the internal organs, thereby leaving the skin to resemble a cold, plucked turkey.

Answer 3

According to this website:

http://www.etymonline.com/index.php?search=cold+turkey&searchmode=none

it means "withdrawal from an addictive substance" (originally heroin) first recorded 1921. Cold turkey is a food that requires little preparation, so "to quit like cold turkey" is to do so suddenly and without preparation.