v. To become a firm believer in something; to accept an argument or philosophy wholeheartedly or blindly.
One top executive named McMahon, the treasurer, was known for going around the company after he met with Skilling, Lay, and Fastow, and they directed him to do some bogus deal and say, 'Well, we've all got to go drink the Kool-Aid.'
You don't follow anyone blindly, my brothers and sisters . . . . We love Marion Barry. He is the mayor . . . . But if Marion Barry disrespects us, we will cry out . . . . We will not blindly drink the Kool-Aid any longer . . . .
This phrase comes from the 1978 "Jonestown massacre" in which members of the Peoples Temple cult committed suicide by drinking cyanide-laced Kool-Aid (although some say the drink of choice was actually Flav-R-Aid).