Well in the first place Lee owned slaves much of his adult life. And in the second, Lee never said anything like that. Certainly not pre-rebellion. Post rebellion revisionist ramblings, maybe. But post rebellion every Southern leader in sight was decrying slavery as a cause.
“If the slaves on the South were mine, I would surrender them all without a struggle, to avert this war.” R.E. Lee when asked his opinion of the view being set forth in the North that the war was fought over the issue of slavery.
An honest assessment of history reveals that Lee inherited 6 slaves from his father. A will written 24 years before his death (and before the invasion from the north) indicated that at that time he had legal title to one female slave. Lee emancipated most of his slaves years before the war, and had sent those to Liberia that were willing to go. Interestingly enough those in Liberia sent very affectionate letters back to him through the lines of war.