Because he's a Psychotic Maniac?

The one thing that has bugged me more than anything else about Goldfinger over the years is this:

Why in the world does Auric Goldfinger kills the American gangsters when he does, in the way he does?

Let's look at the scenario we're given. Goldfinger is using several mob groups to bring in various things he'll need for Operation Grand Slam--they smuggle in the gas canisters, smuggle the Chinese soldiers across the border, etc. They all worked independently of each other, for the promise of $1 million in gold, without knowing any other groups were involved.

Goldfinger calls them all together the day before Grand Slam, and promises them all $10 million if they'll help him carry out the robbery the next day. After a long lecture and some incredibly elaborate displays, the gangster Solo (Han? Napolean?) decides he wants no part of it, so Goldfinger escorts him out, gives him his gold, and has Oddjob drive him to the airport. Except he really has Oddjob shoot him, and compact the car with Solo still in it, and bring the wreck back so the gold can be salvaged from it. Meanwhile, before he can return to the rumpus room from Hell to receive the agreement from the other gangsters, his goon Kisch turns on the gas, killing the lot of them.

Now, maybe I'm dense, but this sequence doesn't make a lot of sense to me. I can understand Goldfinger's wanting them dead. You don't want to leave witnesses, and if they somehow got wind of the fact that their efforts had led directly to a nuke being used on U.S. soil, at least some of them might prove to be patriotic hoods, and turn him in and perhaps have all his gold assets seized while he was in hiding.

And maybe he was just greedy, and didn't want to have to pay off their fees.

But if that's the case, why in the world the elaborate dog and pony show?? Why not gas them all while they're waiting for Goldfinger in the first place??

I know what your first answer is going to be--because Goldfinger is boastful, and wanted to show off his plan to the gangsters before he killed them. But if that's the case, why does he lie about what his plan is? If he's going to brag, why not brag about his true plan, since he's going to kill them anyway?

And why go through the elaborate deception with Solo? Since you're going to kill them all anyway in 2 minutes, why in heaven's name the charade of allowing him to leave? And even so, why the car crusher? Shooting him wasn't enough? Shoot him, take the gold out of the trunk, and dispose of his body with the 15 gassed hood bodies!! And what if three hoods had refused Goldfinger's proposal? Three crushed cars??

So, we have Goldfinger inviting the hoods over, planning to kill them, boasting to them about some plan other than the one he's doing, and killing them before he finds out their response. Even by monomaniacal standards, that's nuts.

I suppose you could argue that Goldfinger was just testing himself, by seeing if he could convince professional criminals to go along with (what Bond immediately sees is) an impossible plan. Or you could argue that since Goldfinger spent all that money making a fancy showroom out his rec room, he wanted to get some use out of it.

But really, there are two reasons why these scenes are in the movie.

The first is, Goldfinger's speech about the "masterpiece of crime" comes nearly verbatim from the novel, and I'm betting screenwriter Richard Maibaum couldn't bring himself to cut it. Of course, in the book, Goldfinger did plan to actually rob Fort Knox, and he did need additional men and supplies from the mobsters to pull it off (plus, he intended to used them as Judas goats). Ironically, the twist Maibum put on the book's plot--it wasn't really a robbery, it was a terrorist attack--made that same speech irrelevant in the movie.

The second reason is, if Bond doesn't overhear Goldfinger give that presentation, he has no idea what's going on, and can't let Felix Leiter know how to set the trap. Remember how spectacularly ineffective Bond is in this movie...he fails in every aspect of his mission. And Goldfinger refuses to fall for the "villain reveals everything to the captured hero" cliche. Unfortunately, that bit of good writing created a conundrum: Bond is completely in the dark, and has no way to get enlightened, unless he overhears Goldfinger boasting. And Goldfinger WOULDN'T boast to anyone who wasn't immediately about to die. So the gangsters HAD to die, or Bond would never know what was going on until he was strapped to the bomb the next morning.

And those are the reasons we had to have the "let's kill all the gangsters" scene, even though it made no sense.

Plus, he was a sociopath. Duh.