But, beyond that, can't we give Matt Weiner the benefit of the doubt in assuming that this was a deliberate choice with no malicious intent?
Malicious intent -- or even conscious intent -- doesn't have to come into play at all, though. A creator can be unintentionally ethnocentric. It's human nature to think in terms of your own group, whatever group that may be -- and thus it is easy to find yourself, if you are white, only writing about white people, completely without meaning to.
Critiques of something lacking in diversity is not the same thing as an accusation of malicious intent. The issue is not whether or not the creator is truly racist in his heart; the issue is whether or not the show ought to have more black people.