I see the point about realism/true-life background, but I was talking about his framing of violence, and in that sense I don't see anything bad in his track record. Across his filmography, in nearly all the instances where the violence is tragic/painful, it is left mostly or entirely offscreen, and even if the style is otherwise broad, it is still used to communicate pathos, not thrill and entertainment (examples: all of Jackie Brown, the opening sequences of Kill Bill 2 and Inglourious Basterds, the flashback murders in The Hateful Eight, the violence against the slaves in Django Unchained, the shooting of the cop in Reservoir Dogs). When his violence is devoid of tact or restraint, it is only when the material itself is broad enough to allow it - see Kill Bill 1, the climactic rampages in Basterds and Django, shooting Marvin in the face in Pulp.
In my eyes, Tarantino has proven time and time again that he understands different modes of movie violence, how it works and should be used in different contexts. There is not one scene of violence in his filmography that I think hits the wrong tone or goes too far (okay, one possible exception - a certain someone getting his head blown off in the end of Hateful Eight). So when it comes to his handling of violence in this movie, I find the "Tarantino is gonna mess this up" attitude to be pretty condescending (like he's some sort of child who we've allowed to play as he pleases before but now after 25+ years he suddenly doesn't know The Right Way); I don't see why he would look at this material and not adapt his sensibility accordingly, like he did all those times before. He's not stupid. And if he is, at least wait until the movie is done and has been in front of your eyes before you claim so.