Are there known examples of ex-McKinsey employees that are generally considered a force for good in general?

The best manager I ever had was an ex-McKinsey consultant. Extremely empathetic, super competent, good dude. I have not worked with him for years but still text him for advice, and he delivers. I suppose that there are people who left McKinsey because they thought they could make more money elsewhere, and people who left McKinsey because they realized they made a huge mistake working there.

Tom Peters’ work on management excellence is generally well-regarded and he started it at McKinsey.

He’s also more recently spoken pretty aggressively about how he thinks McKinsey has lost their way as a business and become a negative force.

Not that well-regarded any more since his fabrications came to light.

Peter Attia's book on longevity is really wonderful, as is his public discourse and research.

Jørgen Vig Knudstorp saved Lego

Jeremy Howard comes to mind. The sheer good that fast.ai brought as free quality educational material feels enough for "good in general" :)

McKinsey has absolutely stellar engineers and engineering leadership in its internal software teams, it's a gift and joy to work with them. Not sure about the consulting side though.