It is a historical error for those who were not there to just refer to August 28th as 'I Have a Dream' speech day. That is a real disservice to those who were there. It was a sad day. It was not a celebration environment.
The essence of America - that which really unites us - is not ethnicity or nationality or religion - it is an idea - and what an idea it is: That you can come from humble circumstances and do great things.