alternate title: Annie's Theory of What Happened
Reality sometimes bites.
Reality: Mr. Gates feels, correctly, that he has earned respect.
Reality: Sgt. Crowley feels, correctly, that police serve an important function and should be respected.
The above facts led to each of the gentlemen in question behaving in a fashion that impinged upon the feelings on the other gentleman.
My simple explanation ignores a bunch of stuff--racism, class, etc..--that might have also been in the mix. However, I'm certain that Sgt. Crowley mostly has easier dealings across racial lines and that Mr. Gates normally has easier dealings across class lines, so that "other stuff" cannot be the primary explanation.
In simple terms, I believe that each of the two nice gentlemen got his feelings hurt and did not know how to communicate the fact to the other nice gentleman.
Better communication skills on each of their parts would have resulted in no arrest, no national uproar, no beer with the president and with each gentleman experiencing generally good feeling towards each other.
Of course, our society does generally frown on tough guys who sob out their hurts to each other and end unpleasant encounters with a hug.