What drives people and groups of people to commit malicious acts?

[Tom]

I have always thought that there is some good in each individual human being. There may be some nasty people out there, but the majority of the time if you get them on thier own, you find that there is a fairly decent mind in there somewhere, no matter how deep.
What I want to know is what drives people to act differently to what they normally are like in different circumstances.
For example, some people are very nice to be with a certain times, but, say when they get into a car, road rage sets in and they are cursing and flashing at other drivers. After thier journey they get out of their car as if nothing has changed and afterwards they are as normal an individual again.
I want to know your opinions on what makes people change their mood and attitude so easily.

Is it when we are in large groups or cities? It is said that people are more stressed on average in the city compared to the countryside.
What other factors are there that affect this that you can think of?
Thanks.

[AL R]

Boredom, malaise, lack of purpose, herd instinct etc, etc, etc.

[Chris B]

Protection of their belief system - which makes up their ego and reality.
thats a thing that must be protected. it's YOU.

[steven g]

They are possibly influenced by their immediate environment when they react to the 'fight' or 'flight' instinct with the fight response. Although In most cases, it seems, it is due to many structural and agency factors influencing their life, and so their actions.

[Lizzy]

Hysteria and stress
People get scared by what is happening around them and latch on to anything that may answer their fears.
Just watch a few speeches by Adolph Hitler to see what the Germans did to the Jews in the 2nd World War. The economy in Germany was at an all time low and people were starving so it necessary to find someone to blame.
Therefor we are all programmed to react aggressively under stress or run away. ie fight or flee

[mailliam]

It all beats me. I said before on here that it will soon be necessary to build asylums for the sane.

http://www.psychologytoday.com/