What he did wasn't immoral. Whether you agree with that or not that's a different topic, and if you disagree with that let me remind you that people have different points of view and that shouldn't be an issue.
Since morality is subjective in the end, the only discussion worth having is whether or not what he did was legal, which it was.
... to you. Like you say in this very comment, morality / ethics is personal / specific to each person.
If you did something legal I despise (I might even think what you did was moral, but still strongly disagree), I understand that you did something legal but still might reject the idea to have you near me or representing something I like and might employ legal means to try to get rid of you, too. By protesting for instance. I have the right to do so as long as I respect the law.
The fact that what he did is legal is settled but he still decided to step out, as a consequence of people protesting against him being the CEO because of his past actions. Since legality is settled and everyone agrees about this, it's not a discussion worth having, actually. Only the rest remains. This is absolutely non-legal concerns that people don't agree on.
Law does not settle everything. Legality is not sufficient for something to be moral. It might not even be necessary.
Now, the rest has also been discussed at length, so it's not clear it's worth keeping discussing this neither.
> morality / ethics is personal / specific to each person
It's not. Almost all of humanity, every culture now or historical, has agreed on many of these things. Others have very wide support, including universal human rights (which include your rights). You can find many arguments supporting these things, throughout human history. Societies and much of the world agree on them (including universal human rights). Research shows evolutionary advantages and connections to these things, and that animals share them with us.
Ethics and morality are not some arbitrary things we each make up.
> What he did wasn't immoral ... Since morality is subjective
I agree that morality is subjective -- what he did was immoral to some and moral to others. Similarly there are people who considered it immoral when CEOs were publicly voicing support for pro-choice policies.
For a leader it probably hinges on the perspectives of the people they lead. You won't have a healthy organization if a significantly large number of people believe you are behaving immorally, especially at a nonprofit paying below-market rates.
> What he did wasn't immoral. Whether you agree with that or not that's a different topic, and if you disagree with that let me remind you that people have different points of view and that shouldn't be an issue.
> Since morality is subjective in the end, the only discussion worth having is whether or not what he did was legal, which it was.
That's a philosophical point, a student's thought experiment taking the (positivist?) requirement for objectivity to a logical extreme - and it's a very incomplete experiment that takes only the first step.
Reality doesn't work that way: Most information and decisions in life are subjective and we have many tools for doing it that way. Subjectivity doesn't make something arbitrary or meaningless or infinitely relative. Almost everything important is subjective, including morality.
Since morality is subjective in the end, the only discussion worth having is whether or not what he did was legal, which it was.