Appalling judgment from both men is the place to start, I think.
On Rock's part, the joke was not particularly funny (GI Jane jokes were weak in the 90s - they are weaker still now) and, crucially, it went after someone because they look weird as a result of their ill health. That could hardly be closer to the bone and, in total, it looked less like a poor quality joke and more like a very barbed insult.
On Smith's part, I don't see a man losing control at all. Everything he did, he just as well could not have done. At no point does he give the impression of being a man overruled by his passions. The odd thing about it for me was the oddly unconvincing nature of it all - not even Rock seemed 100% sure about the intent behind it even as he was joking about being slapped. It was a performance, quickly calculated and pre-meditated in the moment and, for the life of me, I can't work out what on earth he thought he would gain by it. The behaviour of a slightly insecure man, surrounded by flatterers, I suspect.
Why behave so poorly? Well, this is how stars behave - they are rampant egotists of the very worst order. That's why they do the political stuff, for if they bared their true souls, people would run a mile!
The slightly nauseating sense of disorientation that marks almost all the subsequent takes must surely come from the fact that this seemed to touch on things that people think are really politically important - the status of black men, violence among them and men more widely, BLM-style allyship, women's honour and whether that exists - and yet, weirdly, as an incident, it seems to have almost nothing to say about any of it; oddly illustrating the yawning chasm between the world of an unconvincingly politicised media/thespian elite and the issues that they pretend to care about.
Some of the more out-there white supremacy takes make a point of the ceremony being run by an all-black production crew for the first time ever and for this to take place. Apparently, that's evidence of white supremacy somehow. It seems a pretty foolish thing to have given it to an all-black crew anyway as any cock-ups, such as happened with Moonlight/La La Land a few years ago, would then become a "black" failure, as some will probably seek to paint this.