It is true that Lee’s Army kidnapped many free blacks from the Union states they invaded. They believed that they were justified in doing so because of their own runaway slaves.
It is also true that many black US Army soldiers captured in uniform were murdered after being captured by Confederate forces, although there is no evidence linking Lee to this.
Per Jeff Davis, who had some minor position in the pretended confederate government...
“On and after February 22, 1863, all free negroes within the limits of the Southern Confederacy shall be placed on the slave status, and be deemed to be chattels, they and their issue forever.
All negroes who shall be taken in any of the States in which slavery does not now exist, in the progress of our arms, shall be adjudged, immediately after such capture, to occupy the slave status, and in all States which shall be vanquished by our arms, all free negroes shall, ipso facto, be reduced to the condition of helotism (abolute slavery), so that the respective normal conditions of the white and black races may be ultimately placed on a permanent basis, so as to prevent the public peace from being thereafter endangered.”
For good measure - in the same address on Jan 5, 1863, he said slavery was the “cornerstone” of the Confederacy. Here is that part:
“... it ought not to be considered polemically or politically improper in me to vindicate the position which has been, at an early day of this Southern republic, assumed by the Confederacy, namely, that slavery is the corner-stone of a Western Republic.”
It is also true that General Sherman, who married his sister, did not like black people and allowed 700 black camp followers to drown during his march to the sea.