Washington supported legislation to abolish slavery, and although while in office he couldn't formally pardon the slaves at the white house, he freed many of them by the end of his presidency, and he ended up paying all of his slaves and creating lodging for them until well after his death.
slavery is still wrong, but to equate this to Hitler is laughable.
at this time in history, they needed a united front against the British. The BRITISH who actually continued incentivizing the slave trade well after it's economic benefits were running dry. the independence effort meant reconciling with the south, and getting them to join together. to create the union they had to make concessions, but slowly over time the abolition movement gained ground, Benjamin Franklin and John Adams were two men who were entirely against slavery from the beginning.
concession by concession, while preserving the union, slavery was slowly being attacked. in 1860 there was more conflict than just slavery, there was the tariff of abominations that had been done several decades later, and the south had been very much opposed to the north's policy for a while. with the election of Lincoln, there were major concerns about both the north's overreaching influence, and the protection of the institution of slavery.
so the south seceded. interestingly enough, Lincoln isn't the greatest hero. he waited until several years into the war to free the slaves in the south by the emancipation proclamation, but politically he was forced into keeping slavery in the border states. preserving the union he thought was most important, as he didn't want the constitution and the basic rights it espoused to be negated.
in his own personal notes however, Lincoln actually talked about how it would be an atrocity to see blacks and whites intermarrying. the 13th amendment was ratified 8 months after Lincoln's death, and thus began the failed reconstruction era.
now, if you want to condemn slavery outright and say it should have been abolished from the beginning, that's a perfectly fair stance to take. but there's also a chance we wouldn't have ever attained independence if we did.
France had an easier task, as they were fighting within their homes, not against a ruler from abroad. but the 18th century enlightenment revolutions are such a vital part of our modern western civilization, if America had failed, I can't begin to imagine what other course the world would have taken, but one that emboldened the british empire might not have been as pretty.