2) Feel they had wool pulled over their eyes unexpectedly.
Let's talk about the wool. MongoDB was marketed initially with stupid little benchmarks (that were later removed as a policy). Those benchmarks were what people saw, showed their bosses, colleagues and decided -- "this is the one". Yes they picked a bad tool should have RTFM, I would normally say but not for MongoDB.
They marketed themselves as a "database" while at the same time shipping with durability turned off. Yes, you can write very fast if you don't acknowledge that data has hit the disk buffers. I wasn't fooled, I saw the throughput rates and thought, something is fishy. But a lot didn't.
Most of all I have no problem with this design decision given that there is a bright red flashing warning on the front page saying what the default settings are and what it could do to your data. There wasn't.
As developers (programmers whatever you want to call it), we feel that perhaps when other developers market things aimed at us, they would be somewhat more honest than say someone selling rejuvenating magnetic bracelets at 4am in the morning on TV. I think that is where the passionate discussion comes from.