[Kalimac]

Ah, that Gandalf. Mad, bad and dangerous to know, as the Romantics might have said.

I wouldn't call him mad, just brave. Consider Horatius at the bridge; here he was, confronting impossible odds and pretty much guaranteeing his own decease. Did anyone call him crazy? No, and the reason they didn't was because there was NO OTHER ALTERNATIVE.

When you get right down to it, there wasn't much else Gandalf could do. Take it himself? Um, no. Hide it in Rivendell, palm it off on the Elves if possible, or (early on) pray that Sauron never heard the word "Shire"? These are all plans of inaction, basically just delaying the inevitable - one of these days, Sauron would find out where the Shire was (as indeed he did) and then it would all be over. Even Rivendell and Lorien would have fallen eventually once Sauron had found out that the Ring was there and he had laid siege to them. As for giving it to a person - paradoxically, the more exalted and powerful anyone in ME was, the quicker they would fall under its power. Galadriel and Gandalf resisted, but keeping the Ring in close proximity to them would have been like continually yanking the chain of a very nasty pit bull - one of these days it might escape, and then where would you be?

Gandalf also realized that Sauron would never believe that the Wise would let the Ring go off with two non-magical and not terribly powerful little people. They almost say as much in ROTK - something to the effect that two little hobbits sneaking into Mordor are not something that Sauron is expecting, and thus paradoxically much more likely to make it than, say, Galadriel or Glorfindel, whom we can be sure the Eye has been careful to keep watch on.

As for Frodo not being able to throw it in at the last - I think Gandalf may have yielded slightly to a mentality of "We'll cross that bridge when we come to it." After all, he may have reasoned, there was nobody else whom he could trust to even make a reasonable attempt at getting to Mount Doom, and once they're actually AT the mountain, well - who knows what might happen after all. And when you get right down to it, there's no way Gollum could have accidentally stumbled into the Cracks if the Ringbearer had given in somewhere around Emyn Muil.