There is a bit of presentism in the statement, since it interprets Jefferson as he would be interpreted today. There's no question that he meets the definition of racist today, but abolitionism was still in its infancy during his time. Still, he had opportunities to assert the essential equality of races and to attribute what he saw as the "degraded condition" of black slaves to slavery and other sociopolitical conditions rather than race per se. But he didn't take those opportunities. He disliked slavery, but feared emancipation and abolition even more. Benjamin Franklin spent the last years of his life campaigning against slavery, so there were anti-slavery arguments readily accessible to the "Founders." But they chose to ignore them, and in the Age of Enlightenment, they should have done better.

Main source: Paul Finkelman. 2014. Slavery and the Founders: Race and Liberty in the Age of Jefferson. 3rd Ed. NY: Routledge.