I have argued in the past that those who charge the Republican party with epistemic closure forget (conveniently or not) that there is plenty of epistemic closure in their ranks as well. But this does not mean that epistemic closure amongst Republicans should not be criticized.
So, let me go on record as stating that cherry-picking a convenient media forum for debates between Republican presidential candidates is a bad idea. I recognize that Republicans would like to have friendly moderators ask friendly questions of their candidates, but eventually, those candidates are going to have to confront potentially unfriendly moderators. Best that they learn how to joust successfully with unfriendly moderators early in the campaign; honing that particular skill from the outset could be useful to the candidates and to Republicans in general as the campaign goes on.
And let me also go on record as stating that purging Republicans who happen to disagree with certain planks in the Republican party platform is a really terrible idea. (Link via Charles Lipson.) Winners can afford to purge their ranks. Losers cannot, and given that the Republican party has picked up the unfortunate habit of losing elections, it currently qualifies as a loser party. To win, it has to expand its tent, not shrink it. And incidentally, whether or not one is a same-sex marriage supporter (and I am), who in their right mind thinks that opposing same-sex marriage is a political winner these days?