terrorism has people afraid in general so any threat-whether it be a major event or just being mugged on the street-people would rather see dealt with using brutal force for a false sense of security
a lot more 'us vs. them' and the definition of them seems to expand every day.
i also think that white flight is a contributing factor-in NYC, you used to have to live in the city to work on the force. once that was lifted, i think that changed policing a lot. not to say that po-po were actually living IN the areas they policed but there's a familiarity that was lost and definitely more of an understanding that keeping an area safe keeps surrounding areas (where they likely live) safe.
not to say shit was all peachy but things you hear older cops say now about how these young cops aren't really being introduced to the community like they were when they started. older cops would ride them around and point things and people out and it doesn't look like these young cats are getting that. i'm sure a lot of these older guys still working were around when crack was at its worse so they likely regard the people they police as savages not worthy of interacting with which is sad.
this isn't to say that there's more brutality now. i really don't think there is-killing perhaps but i think it's just an issue of it being more high profile and with evidence that clearly backs up how unwarranted the situation was. a black man getting lumped up in custody or while being taken into custody isn't something new.