Drinking the KoolAid - WTF?

[dreamshark]

In the last couple of years I've been encountering this phrase more and more often. I'm baffled by it. I just heard it again on the radio: somebody talking about having mistakenly expected a particular sports team to win and described himself as "... drinkin' the green KoolAid." I THINK he meant that he had been deluding himself (I don't know why the KoolAid was green, however. Is green the Celtics team color?). I've heard it in business speak a number of times. "We've been drinking our own KoolAid" or "We want them (our customers) to keep drinkin' our KoolAid."

Does anybody know what this means? I can think of two vivid historical references for KoolAid, but in one case the KoolAid was laced with poison for a mass suicide, and in the other case it was spiked with LSD to make the bus trip more fun. And both of these things happened decades ago - why is the KoolAid terminology popping up now? Did somebody just write a book featuring KoolAid as a brainwashing tool or something?