After having suffered through many a battle and b&m session on various forums for well over a decade, I think you can break the piss and moan types into a couple of basic groups:
1. Newbies who are two lazy/impatient to rtfm and want instant answers.
2. Crotchety old users who insist that the best camera ever made was the Such-and-such Promaster 4000 and everything since has been a decline into an equipment (and moral) cesspool.
3. Idiots. Some people are just not very bright and frankly shouldn't own complicated devices. Often hard to tell the difference between this and #1 though.
4. Pot stirrers and gear freaks. They don't actually shoot pictures (other than brick walls) but rather own cameras to impress friends and more importantly, slather over Canon while slagging Pentax under a veneer of impartiality.
5. People who are drunk. Note that #5 can be applied to 1-4 as well.
6. People who actually have a legitimate problem or miss a particular feature that is important to them.
The problem is that most think they are #6 when in fact they are one of the other ones. As for me, it is after noon, I'm on vacation, so I'm going to have a drink and strive towards #5