Rob does a capable job dismantling a pretty pithy Weekly Standard article about David Mamet's movement to the right. As someone who is pretty avidly interested in Brecht, I agree with everything Rob says.
Allow me to add a few points as well.
“His protestations [against capitalism] were not borne out by his actions, nor could they be,” Mamet writes. “Why, then, did he profess Communism? Because it sold...The public’s endorsement of his plays kept him alive; as Marx was kept alive by the fortune Engels’s family had made selling furniture."
Firstly, any close reading of Brecht makes it pretty clear that among communists, he was very much a populist. His plays sold because one of his central tenets is that theater needs to be popular, among the people, and communicate with them. Whether or not he was interested in the money is something I can't speculate on, but I can say that there's no need to cry "hypocrisy" there, because he truly felt that in order to be true to the people you needed to reach the people. "The proof is in the pudding."
Secondly, if Brecht was purely interested in self-advancement, he could have made some better choices. For instance, when the tides of German history turned against communists, and many communist artists were jailed or executed for their beliefs, he could have done what many others did -- become a Nazi. That could have made even more money. (By the way, if you want to see what that would look like, you should see another excellent play by a "lefty", Tony Kushner's Bright Room Called Day.)
And then, in the United States, when he was called before the House Un-American Affairs Committee and accused of being a communist, he could have done what other profitable artists did at the time (such as Elia Kazan) and walk away from any of his beliefs or associations that were inconvenient. Instead, he left the country where he had his greatest financial successes to go to a communist country (East Germany)?
Brecht comes across as a hypocrite if you read him as a strict ideologue; which, I imagine, more suits his critics than himself:
Although a cold-blooded—indeed bloody-minded—advocate for public ownership of the means of production and state confiscation of private wealth, he always took care to copyright his plays.
If you were to apply the adjective "cold-blooded" to anyone, Brecht would be a poor fit. He's incredibly hot-blooded; he yelled at himself in rehearsal, insulting his own work, he wrote fiery essays that were intended to stoke controversy, and he rebelled against the idea that human beings were internally consistent or had consistency of character.
His characters in his plays are not the ideal, communitarian communist drones that you can find in a communist play like most propaganda. Instead they're often drunks, rogues, people who play eccentrically with the law, who are selfish and look out for themselves and somehow do good for other people in spite of themselves.
So yeah, aside from all of the problems Rob pointed out about how odd it is to define Mamet in relationship to Brecht, it's revealing how much of the article is based on this notion of Communists as homogenous ideologues, who are somehow more popular than other ideologies. I'm sure being a communist in the first half of the century was the "easy" choice.