To make a wholehearted, unconditional commitment (to some group, or idea, or plan) in contrast to choosing an alternative. It emphasizes a resolute decision (good or bad) in response to a choice.
This is a reference to the "electric
Kool-Aid acid tests," which were LSD parties held in the San Francisco Bay area in the mid 1960'
s. Someone who was willing to drink the LSD-laced
Kool-Aid had, symbolically, made a choice to join (if only for a few hours) a counterculture that stood against conventional
society. Once you take acid, you're committed -- the trip lasts for hours and you can't cut it
short or change your mind. Once you've drunk the
kool-aid, you're firmly committed.
IMHO it is not about suicide: kool-aid isn't a symbol for poison.
Coach got his players to drink the kool-aid.
I really
like Macintosh computers; I've totally drunk the Apple kool-aid.
That berserk guy who tried to
kill people at the Tides Foundation really had drunk the kool-aid that the right-wing media were serving.