The most despicable word known to mankind: 'power' .
Because they believe they can get away with it.
They feel stronger because of the numbers. Also, when some feelings are shared they increase. Stupidity is a feeling lolz
For some bizarre reason, when ever people join together in a group, they will always want to put the blame on their woes on the odd person. <br />
I would have to say that it is due to the power and safety in numbers, and the vulnerability of the individual.
They don't care if it's "moral". They are serving a larger agenda and will often do whatever it takes to shift the blame or accomplish what they want.