Elizabeth Anderson and others are ignoring the very history they purport to support. Those statues (which Lee himself opposed the idea of) do not honor Lee the man or his earlier actions; they explicitly glorify his conspicuous acts of treason in support of institutional racism. Depicting him (and his fellow traitors) in Confederate uniforms makes that clear. So does the fact that the vast majority of them were erected in the early 20th century, during a time when the KKK and racist sentiment were ascendent in parts of the USA. 
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The issue of who did or didn't own slaves is a complete and obvious straw man. The issue is honoring traitors for their violent, deadly acts of treason against the USA in the name of a philosophy which was ascendent at the time of the treason and the time the monuments were erected but is now considered morally repugnant. And whether such monuments should occupy civic locations like public parks, courthouse grounds, and the like.