Are you past or present employee? If so, then you probably know better, but I can only response to what I know, and I was never related to Basecamp.
What you say is correct in really bad situations. Thing is, that I have trouble to see real issue in what has happened here. It somehow feels surreal that DHH and Jason were able to fool us all for years, and now it seems that they are being accused of almost being hostile to their employees.
Everything arose around this darn name list. How this ended up with using words of "white supremacy" is beyond me, and genuinely feels as words misunderstanding or misuse. In a team with non-natives, it is extremely easy to have such misunderstandings. But it is also easy to not spot that misunderstanding quickly. And that someone misunderstood something is not a reason to apologize I believe.
Also the way they tried to handle the situation, seems to me like they were stunned by it and it took them off guard, because they are probably not racists guys, and instead they are fully and deeply against such people. That's why further developments seem more random than professional or done on purpose.
I just had a situation in my team where we had a junior guy that we wanted to train. He was very hesitant to learn, he always knew better, and any PR feedback ended always with 2 hours-long calls, trying to explain him the comments there. He was always told that we want to get feedback from him, that he always will be listened and he was always assuring us that he is fine, that he finally understood the feedback and all.
Guess what - today he told me that he leaves and the main reason was that he could never understand the PR and that he never could agree with it, and that he always felt that he can't say word and that he has to obey..... I'm feeling confused and cheated all day. I went far and beyond to make him feel as comfortable as possible, it took many overtime hours to stay with him to discuss stuff and then go back to do my tasks. I'm speechless right now, and trying to not loose my self-confidence as I literally don't know what I've done wrong.
I feel that their situation might be somewhat similar now:
1. Apologize - but maybe they don't see what for?
2. Correct the wrong - but what was wrong?
3. Allow the space for employees - what kind of space? How are they not allowed for that already? Do you mean doing some sessions and commit weeks to try to solve people's own issues?
4. Get employees back on board - ok they messed up with this one by posting the policy change publicly.
Not sure it was noticed, but DHH hasn't tweeted once in May. I obviously don't know the reason, but maybe, just maybe, he is trying to put all the pieces together to at least have an idea what just happened?