They are given a power over their fellow man and they have proven time and again to abuse that power for their own personal gain, and in some cases simply to show their authority over others. They do not abide by the laws they are hired to enforce on others, and they cover for eachother when laws are broken by fellow officers.

Law enforcement does what they want, when they want, with no fear of consequence. It may not be all of them, but when the public notices and witnesses a continuing trend, they begin to assume all law enforcement acts this way.