I didn't feel like reading through everything, so pardon if I missed something.
I don't fear 2012 for any doomsday reasons. I worry about it for strictly scienific reasons.
Here's why:
The sun has cycles in which it releases massive amounts of energy. This cycle, if I remember correctly, happen roughly once every 11 years. These cycles also have cycles within itself, meaning some peaks will be stronger then others. The strongest one thus far is set for late 2012.
Now, normally, it wouldn't be much of a problem. But its also coincidently timed with something else projected to happen in 2012, polar reversal. (See:
http://en.wikipedia.org/wiki/Geomagnetic_reversal)
Many scientists fear that polar reversal is occuring at a much more rapid rate then previously thought, and predict it may happen soon.
Now, just think about it.
Weak magnetic fields that normally protect us from the massive amounts of electrons (energy) throw at us by our sun will be at their weakest (whether or not polar reversal occurs anytime soon, we're still as weak as we've every really been during the course of human history) while the suns cycle is at its strongest.
Something like this, but worldwide.
http://www.ips.gov.au/Educational/1/3/12
Now, its by no means catastrophic. Nor would it even nearly mean human extinction. But it'd be a pretty big incident.
But at any rate, 12-21-12 will be pretty bad if people start looting and rioting all over the place,which is totally plausible, with all the media attention the date's been getting lately. God only knows it'll pick up.