If she actually gave them a detailed, logical rundown about the Borg right off the bat, it wouldn't get across the basic message of 'the Borg are supreme badasses and the crew is in some deep shit now' quite as powerfully as, [I wrote:
"all I can tell you is you better start heading back RIGHT NOW"[/I].
Eh, probably right. But then it's all strictly for dramatic purposes. Yeah, she COULD tell them who and what the Borg are and what they do, but... nah, let's save it for an exciting and dramatic reveal in Act Two.
Yeah, it makes for a great eps. But hard to understand in RL terms.
The Enterprise being tossed into Borg space unawares was essentially a certain-death situation, unless they were lucky to leave RIGHT NOW.
I think of other RL situations where one might be in a certain-death situation (Pearl Harbor on Dec 7th, Mexico City earthquake, Hiroshima, and so on)
If you knew the situation was pretty grim and people asked you for help and info, and you KNEW the circumstances, wouldn't you offer something more than "you'd better leave RIGHT NOW" ?
If you knew the circumstances, wouldn't say right away "there's a huge tsunami coming" or "a terrible bomb will go off today" or "an air attack is headed towards us"
or "a tremendous earthquake will destroy us" ?
I still think Guinan should have spilled the beans about the Borg from the get-go. Less dramatic, sure. But seemingly more reasonable to me.