On his always interesting and engaging blog, Robert Philen has posted an important piece called "Enlightenment Values"arguing against the currently popular tendency to denigrate or dismiss the universalist values of Englightenment humanism because its founding figures didn't always adhere in practice to their own values. Philen points out that the fact that the actions of some of the framers of the ideals of the Enlightenment didn't always live up to those ideals doesn't negate the value of those ideals. In fact, this critique of the Enlightenment is itself based on the very Enlightenment values whose hollowness it claims to unveil.
The prolific historian J.M. Roberts makes the same point about both Marxism and Christianity in his book The Triumph of the West: "The appalling practical outcome of the installation of Marxism in some countries as a state religion no more affects [the judgment that Marxism restates and summarizes some of the West's most central ideas] than scores of historical examples of institutional Christianity acting in a repressive, uncreative way in the past nineteen hundred years nullify the central messages of the Gospels" (80).
As Philen points out, "The fact that Thomas Jefferson was a slaveholder doesn’t undermine his words regarding liberty and equality. It makes him a hypocrite, something he himself was aware of, but it doesn’t and shouldn’t make his words in the Declaration of Independence any less stirring (nor do you have to be a communist to be stirred by the evocation of those very words by Ho Chi Minh against French colonialism in the mid-20th century). Nor was his slaveholding a part of an Enlightenment Project. Instead, this was a practice resisting such a project and contradicting his own stated values."
I encourage everyone to read this insightful and bracingly sensible piece.