The main issue, as I see it, is that they have a lot of capacity, opportunity and incentives to misbehave, and very few or very weak consequences for doing so.

Over time, this leads, of course, to more abuse of power.

Yet, in spite of the above, there are still some good reasons to give cops a lot of power and few consequences for their actions. If they didn't have the means to react to threats or constantly faced the prospect of punishment for their actions, they would simply stop doing their job; in the developed world we see that in the places where they won't go because they're afraid of the reaction (either legal, in media, or violent). In many places in the Third World this happens where cartels, gangs or terrorists retaliate against them routinely.

The problem is that, where they have little to no fear of consequences, some will inevitably abuse their power. How to balance both negative extremes? I don't really know.