What purposte does it serve to say than man is essentially good, or essentially bad?
Say what you want, but we have to deal with both varieties, every day. Most commonly, the people we meet are a combination of both good and bad tendencies.
I'm perfectly happy to let it go at that.

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That a good criteria for how to pick a candidate to support..

Nevertheless I am getting a lot out of reading Mamet and the Roger Simon piece.

I notice one distinction is that we often conflate means and ends. I might support liberal ends but also conservative means. For example I support the dramatic reduction of all pollution including green house gases. Meanwhile I support using the trading of carbon credits or a carbon tax to influence the market place.
Likewise I prefer better schools but also think that vouchers should be given a more through test.
I think a lot of us in the middle of the political spectrum share and prefer this kind of flexibility.

That Sowell would be called a philosopher when he is a political columnist, and then appended with 'greatest'- not even mere 'great', pretty much undermines the intellectual credibility of Mamet's argument; a man who, himself, is not particularly known for his great philosophic stances in his writing, short of profanity and stereotypes.

I began reading not only the economics of Thomas Sowell (our greatest contemporary philosopher)

That's a guffaw-inducer.