Re: Police Abusing Powers
It is more correct to say that some of its findings are controversial, since there is not a consensus amongst research psychologists. The main issue is that the study was done once, terminated early and can never be repeated in an academic setting, at least in a civilized country, because ethical approval is now mandatory for human experimentation in academia. Consequently criticisms cannot be addressed by repeating it with a modified protocol.
Recent attempts to emulate it have been geared towards things like reality TV etc which don't require ethical approval, and lack scientific rigour since their goal is entertainment, for example this one. Incidentally, this particular emulation was also stopped because of the effect on participants.
But you don't really need a psychology experiment to observe that if one group of people is given more or less limitless power over another group of people without adequate oversight, then the results are often unpleasant. Particularly as square pegs gravitate towards square holes when it comes to making career decisions. See the torture and prisoner abuse by members of the US 372nd Military Police Company in Abu Ghraib for a relatively recent example.