Why did all of the Scoobies just assume Buffy went to hell when she died?

I mean, she dedicated her life to fighting demons. She was a good, kind person. She literally sacrificed her life to save the world from evil. If she wouldn't be sent to heaven, who would?

If I were Buffy, I'd be pretty damn insulted that my friends were all convinced I'd have been damned to hell.

Her body hadn't been sucked into some vortex like Angel's was. For all they knew, she simply jumped to her death.