I believe that there are some trends worth mentioning.
1) It seems to me that police in small towns tend to be more like Sheriff Andy Taylor, and police in larger towns tend to be more like Barney Fife... or Judge Dredd ("I
AM THE LAW!").
2) It also seems that younger police officers are more likely to favor police and state power and less likely to respect our constitutions and the individual rights of those taxpayers who pay their salaries, and older police officers are more in the "peace officer" mode than the "law enforcement" mode.
3) Finally, it seems to me that the problem with bad police officers is increasing over time, which I find disturbing.
Of course, like all stereotypes, there are plenty of contrary examples, and my opinions and observations are subjective and are almost certainly skewed at least a bit.
To the original question though, I think much of the concern over police behavior in the open carry community is the result of some bad first and second hand encounters, bolstered by high profile videos like this one.
http://www.youtube.com/watch?v=GpC3-2ATmIo
(6:15 video - Warning: Bad Language)
This police officer wasn't disciplined for this egregious behavior, but was finally fired after he spent a long time berating passengers in a back seat of a car, then realized that the driver had a CCW and was carrying. He became insane with rage when he realized his mistake, and repeatedly threatened to execute the driver, despite the fact that he had repeatedly told the driver to shut up when the driver repeatedly tried to show him his CCW permit and inform him of his lawfully possessed weapon as the Ohio state law requires.
http://www.youtube.com/watch?v=DaDP8YLCKj4
(2:35 video - Warning: Bad Language)
Here's the full video. It's disturbing.
http://www.youtube.com/watch?v=VG2TSCpSEVw
(15:30 video - fast forward to 5:00 to see the attitude related to those who aren't police but are armed)
This is an example of what it finally takes to sever the thin blue line that protects police in Canton Ohio.