Disorderly Conduct and other subjective discretionary laws.
I do not see this as purely a race issue. Prof. Gates most likely 'jumped the gun' due to past experiences that ultimately escalated into a race issue fueled by the media.
The bigger picture is that unfortunately our law enforcement agencies have vast discretionary powers and really think that they are above the law and our Constitution. I fear that we are slowly but surely regressing towards a police state. I am originally from Africa and what I see here is that law enforcement is not really dedicated to 'Serve and Protect' as commonly advertised on their vehicles. What it really should read is: 'To Intimidate and Harass' - Ask any teenager in southern California - and of course to make arrests so that the wheels of the Judicial Industrial Complex can keep turning.
Of course this has ultimately become a race issue but basically this was just cops being cops.