Just a quick note on form: your post looks copied and pasted. I think it's the way you make factual assertions as though you yourself were a reliable source. "Some police officers come to see themselves not as simply enforcers of the law, but as the law itself"? Do you have psychological studies to back this up? Moving on from the tone, if you're going to put a sentence in quotation marks you should really mention who it's quoted from. I can find quotes to rationalise genocide but they're not from people we ought to be listening to. And it's really difficult to take a site seriously when it's called "abuseofpower.info"; even if the information on that site were sourced (which it isn't) the site name gives the impression that it would be cherry-picked and presented with bias.
You say "In any given year, there are about 10 million people held in pre-trial detention in the world’s prisons and jails." That appears to be false. Googling "global prison population" beings up first this BBC page claiming the total number of people incarcerated around the world - pre or post trial - is around nine million and then this, presumably more up-to-date, page prisonstudies.org which doesn't give a total and can't be added up in less than thirty seconds (spaces in the numbers mean Excel doesn't work :/), but does give totals for individual countries which are not much higher than the BBC page's totals, and therefore the overall total is presumably still less than ten million. I can only assume your figure includes North Korean internment camps or something, but I can't confirm this because I can't find that number on either of the sites you linked. To be fair, apparently 90% of people imprisoned in Libya are unsentenced, so there's still more globally than there should be, but the global mean is 33% so the untried total should be about 3 million. I'm not sure this affects any of your points but if you're going to present your post so authoritatively it needs to be true.
The IJM site you cite claims at one point "nearly 30 million children, women and men are held as slaves". I question any definition of "slavery" which produces a total number of slaves higher than the global prison population.
The main thrust of your post seems to be that police in the developing world tend to be corrupt. I would argue that the problem there is not the policing system but the economy. The police are in a position where they feel that the only way they can make money is to extort it. You would probably have found the same thing amongst law-enforcement in the pre-development Western world. That doesn't mean they're not arseholes, but it means that the solution is not to be found in a debate about law enforcement.
You say, with underlining, "The sad truth is that the police can abuse their power and they will. And I don't think there is much we can do to change that." I disagree. As Skeletonxf said on the first page, one solution is to have the police wear cameras. Complaints against officers apparently dropped by 80% in Rialto, California after the police started wearing cameras, although obviously one city's results aren't enough to generalise from.
I think there must also be some kind of cultural problem with US police in particular. I've had to speak to police in the UK on several occasions, and once in Belgium, and every time they've been polite and helpful. I can only speak for myself, but I very rarely hear bad things about the police around here, whilst American police are always being portrayed as racist bastards who would lock up every civilian they could get their hands on given half the chance. I don't know what that cultural issue is exactly (although I'm going to look pointedly at the lethal weapons US cops have strapped to their hips) or how to fix it, but to the extent that the problem is cultural it isn't an inherent problem with law enforcement itself.
In conclusion, fuck da police. They do a difficult job and they deserve a good time once in a while.