As an example, I'm on the neurology faculty. One colleague is an academic activist in the sense that she educates, develops programming, and sits on several committees dedicated to ensuring that historically marginalized groups realize that neurology is a career possibility for them. It gets results, and it's not just self-validating. The claim that belief you can help someone assumes your own superiority is unfortunate.
You say that your colleague's diversity-focused activity gets results, and my question is: what results? A more diverse body of students studying neurology? And if that is the answer, then who cares? What is your argument that increased diversity makes neurology or science better?
If diversity is your objective function, fine. But there are other goals to pursue, and which should be pursued in academia by faculty. I think diversity is very far from what should be the top priority.
The advantage of diversity is that it is an easy metric to understand, pursue and make gains in.
The results are two-fold: most directly, more members of marginalized communities pursue and are successful in the field. More distally, clinical outcomes (patient return, treatment plan adherence, and medical outcomes) are higher when patients see doctors with a shared historically marginalized status, particularly race/ethnicity. That's borne out by the research. So increasing the diversity of the workforce enhances outcomes in diverse patient populations.
Your view is just overly jaded. There are data backing all of this up. It's not just done out of a feeling or a PR move or meaningless corporate metric (though those things indeed contribute to the motivation in a lot of cases).