Although allegedly this is the movie's "suppressed ending", I wrote it myself, admittedly influenced by the Saturday Night Live sketch in which they went over to Potter's house and beat him up.
Coincidentally, the Bible quote with which I notionally end the film - "therefore choose life" - was also in Al Gore's Nobel Peace Prize speech yesterday.
The challenge we all face is that of continuing to choose life, even while recognizing that we live in Pottersville, not Bedford Falls.
It's A Wonderful Life - The Final Scene
Potter's personal health care attendant (the man who pushes his wheelchair) bursts into the party at George and Mary Bailey's house. The mood, which had been festive (just a moment before, we saw the arrest warrant being torn apart and thrown on the pile of contributions from "so many friends") changes immediately, as the tale of Potter's purloining of the disappeared bank deposit is told. At first incredulous, the people become increasingly angry as the depth of depravity of the twisted, misanthropic millionaire becomes clear.
Next we see the crowd carrying torches as they approach Potter's mansion - it is like the evil twin of the house that George, Mary, and their kids have filled with love - equally large, but almost all in darkness, and without any sort of holiday decoration, neither Christmas tree, menorah, or solstice wreath. Ernie drives up in his cab, and siphons some gasoline from the tank into a large metal can. We see him and Potter's former health care attendant splashing the gasoline at the entrances of the house, including the wheelchair ramp. Uncle Billy ignites the flammable liquid by throwing his torch into it, and the rest of the crowd follows suit. The volunteer fire department arrives, but Burt the cop keeps them from coming up the long drive.
Inside the house, through the windows, we see Potter desperately going from room to room, trying to escape, but it is useless. Uncle Billy watches with grim satisfaction, and we see the flames of the house reflected in his glasses as he mutters "So long, you old so and so."
We recognize other members of the crowd - the same individuals we saw in the "Pottersville bar" scene - and, like then, there are no women or other members of the Bailey family present, except for Uncle Billy.
Clarence the angel, no longer in civilian clothes, but rather in his magnificent new robe and wings, watches sadly from treetop level. The camera pulls back and we see the house beginning to collapse as the flames leap higher. The final scene pans upward from the burning house to the starry sky, and we see in Gothic letters the following Biblical quote: "I have set before you life and death, blessing and cursing: therefore choose life" (Deut. 30:19).