Founding Father and Slave Owner

I was reading an article on Ron Chernow's biography of George Washington, which is one of the better biographies I have read, and that nagging question came to mind again.

How could any of the Founding Fathers, writers of the Declaration of Independence, architects of the words "all men are created equal", "unalienable rights" and "Life, Liberty and the pursuit of Happiness" possibly find it acceptable to own slaves?

Perhaps they did not view their slaves as "men" and therefore they fell outside the rule of their new union. It wouldn't have been the first time nor would it be the last that the interpretation of a powerful majority would determine who got to live (the Salem witches), or vote (women of the early 20th century) or be free.

Or as Chernow hints, Washington and others may have believed that the viability of the newborn union was so precarious that to force the southern colonies to end slavery at that time would itself doom their entire endeavor of independence. Believing this, they decided that the the creation of an independent nation was more important than the freedom of a few thousand slaves at least for the short term and that the loss of the war for independence would in any case render everyone, free man and slave, in the same dire circumstance.

If only Mr. Peabody could fire up that WABAC machine.