It depends largely on the source and how that source defines his qualities.
Some (wrongly) declare he hated the practice, and some (also wrongly) declare him the Big Bad of all racism in the South ever.
Both are half-wrong. Though the notion that there's a shitload of Southern propaganda painting him as a hero and bringing him up on a pedestal is completely correct. There's a lot of bullshit to sift through about this guy, which is why you'll see I refer to his personal letters and writings more than those of the press at the time.
If there's one thing from the propaganda that's somewhat accurate, it's the "fought for his state despite [misgivings]" thing. Lee was actually against the secession, very vocally so, but he was democratically outvoted by his people. After that, he went into a mindset of "I don't like their choice, I don't agree with it, but my people have spoken so I'll fight for what they've chosen."
Which is commendable as far as sacrificing personal pride/stakes for the greater perceived will/good of one's people goes...but there is a line between valuing the votes of many over the dissent of one and going all with horrible things. While the mindset the guy had over this particular thing was admirable, the actual context just shows how misguided his moral fiber was--would seem he'd rather let a thing he knew to be terrible and would cause huge problems occur than be a dissident and stand against it. This was a bit of a running theme with Lee's moral compass.
From his letters (which I can track down and cite if necessary), it was not a case of "I hate slavery" OR "slavery's good because fuck these people." His writings tell of a mindset wherein he considered it a "good thing" for the black populace.
He did indeed view them as subhuman, but not necessarily in a malicious light. The same letters belay a stance where he believed them to be "unfinished" and in need of tough lessons and hardship to progress the race forward, albeit this sentence is paraphrasing the hell out of it. He believed this "hard lesson" to be the practice of slavery, and believed it to be greenlit by the man upstairs--ergo, the letter says in similar wording that "yeah, slavery's got some pretty deplorable shit happening to these people, but God's basically allowing it to happen so it must be part of his Plan for these people and as a godly man it is my duty to carry out this practice even though I'm fully acknowledging there's some inhuman cruelty going on within it."
Now despite being a Southerner, I'm by no means a Lee apologist or rationalist. I just prefer for facts to be reasonably straight and/or, more importantly, people throwing around accusations throw them around properly and fairly. Lee was by all means a racist, but by his own writings he seemed to be more of a "oh these poor savages, I must help advance them as is my place as the Holy White Man™ in the service of God" kind of racist than the "blacks aren't people, fuck them, they deserve violence and pain and death and hatred, fuck all of them, they can all die for all I care" kind.
Neither's good, but I would argue that one (the latter) is considerably more dangerous than the other, since the former at least MARGINALLY comes from a place of thinking one's being helpful. Unabashed hatred and misguided zeal are both dangerous and problematic, but misguided zeal has a bit more chance to be dissuaded and talked down than blind hate.
Now I'm completely ignoring all the other facets of the guy's character--whole bunch of sources, some again by his own pen, that illustrate a complex individual who was neither wholly good nor wholly evil (as is the norm with hated historical figures). We've got letters to his wife talking about how doing good is what makes life valuable and his own measurements in that department filled him with despair, which corroborates the aforementioned mindset he seemed to be in, and other such things. None of it justifies what he did, but I'm not a big purveyor of tunnel-focusing on a singular aspect of a person when debating their quality of character, no matter how horrible that singular aspect is or was.
But the whole statue situation's pretty much a simple thing for me--I fully understand and endorse wanting to remove honorable trophy-type representations of people who performed or oversaw horrible acts of inhumanity. I really do. I'm from the South, and every Southerner has to make peace with that war sooner or later in some fashion, and I'm on the side that wants to learn from the mistakes and horrors rather than take the easy route and just repeat them.
But at the same time, I'm very much against what can eventually amount to historical censorship--remove all the remnants and reminders of the horrible things we've done in the past, and what's left to learn from and teach us not to repeat? Take the thing down from its pedestal, that's one thing, I'm agreeable to that. But destroying it? That just sweeps a nugget of history under the rug because it's unpleasant. And I'm not okay with that.
Plus, there's a GRAND irony in the fact that Lee openly stated he didn't want any statues of himself made when the war was over, out of a worry that it would cause the wounds of that war to never close and keep reopening and keep people unable to move on from the mindsets that led to all the atrocities--lo and behold, the old bugger was spot-on. Who woulda thunk it?