He's not guilty of genocide, or even murder, so there's certainly much higher bars that can be set.
But I have a deep aversion to trolls. They cause pain deliberately. That pain is diffuse and hard to account, but so widespread that (a little bit) times (a lot) adds up to a large number. And I think it's pretty clear that Musk enjoys inflicting pain on people.
Perhaps that's too low a bar to set for the title of "terrible human being". But that's my bar, and he sails right over it. I tried to ignore it for a very long time, and I'm not sure how much longer I can.
He's also running a company that is making enormous strides in getting the world off of fossil fuels -- and pushing others to do the same. (I have quibbles with continuing the multiple-cars-per-household lifestyle, which I think will need to be reconsidered if we're going to stabilize our effect on the environment, but at least he's doing something -- and it includes reducing fossil fuels in areas besides transportation.)
And he's running a company that is revolutionizing space transport. I don't believe in his goals there, but I think good will come of it. He's doing it for real, not just running his mouth off.
And yet, on balance, he's contributing to an American social climate which keeps nudging closer to literal civil war. You probably think that's hyperbolic, and perhaps it is, but it's undeniable that its making a lot of people angry a lot of the time. He's in a position to know better, and it looks to me as if he enjoys it. To me, that merits the designation "terrible human being".
You can legitimately disagree with that, but I think we can agree on the reasons I say it.