You can decide to read what Sam Altman says and say "but maybe he doesn't really mean it", but that's a bit of a stretch. Just read their actual thoughts on the subject. tptacek is not misrepresenting what they are saying.
From Altman:
"His racist, isolationist policies would divide our country, and American innovation would suffer. But the man himself is even more dangerous than his policies. He's erratic, abusive, and prone to fits of rage.
He represents a real threat to the safety of women, minorities, and immigrants, and I believe this reason alone more than disqualifies him to be president.
[...]
Trump shows little respect for the Constitution, the Republic, or for human decency, and I fear for national security if he becomes our president."
I am not saying he doesn't mean it, simply that he doesn't mean it enough (it would also be an absurd claim to compare Trump with Musolini) to do anything about it.
From Altman:
"His racist, isolationist policies would divide our country, and American innovation would suffer. But the man himself is even more dangerous than his policies. He's erratic, abusive, and prone to fits of rage.
He represents a real threat to the safety of women, minorities, and immigrants, and I believe this reason alone more than disqualifies him to be president. [...]
Trump shows little respect for the Constitution, the Republic, or for human decency, and I fear for national security if he becomes our president."