Maybe Gates just snapped. Just was having a bad day. Just couldn't take it anymore. It happens. Maybe he has a history of depression and anger issues.

I'm sane, employed and a productive member of society but stupidly argued with the cops twice in my life. They always win. Now -- even on my worst day -- I will do whatever they say...yes officers, yes, sir, how can I help you sir.....

Posted as a comment in today's PD coverage, this seems to me to be the best explanation for what happened to Henry Louis Gates. 

I will never feel the weight of his personal  history on my own back, but I can empathize with  faulty decision-making and "having that really BAD day."