The clue is in the title!
Arguments about MAF are pretty nonsensical. The clue is in the NGO's title! And they do a hell of a lot of good even for Sir Bob Geldof.
Tis a bit like suggesting a preist or the pope's role should be open to anti Catholics!
That said I've not seen any atheistic groups excluding God believers from their "higher" echelons - but why would someone want to?