One lasting legacy of the Jonestown tragedy is the saying, “Don’t drink the Kool-Aid.” This has come to mean, "Don’t trust any group you find to be a little on the kooky side." or "Whatever they tell you, don't believe it too strongly".
The phrase can also be used in the opposite sense to indicate that one has embraced a particular philosophy or perspective.
Bob: Yeah, he really drank the Kool-Aid on that one.
Chris: I'm thinking about attending a PETA rally
Donna: Whatever you do, don't drink the Kool-Aid!
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.
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.