I am neither a 'scholar' nor a 'brother' (why do so many gentlemen here keep on excluding female opinion in their posts?!) but here's my two cents:
1) In verse 5:5 the Quran is deliberately making it almost impossible for believing men to marry a non-momin: It demands that a woman from the People of the Book be both chaste and (elsewhere) a monotheist under Quranic criteria.
2) Believing women are told outright that they cannot marry anyone but a momin (2:221). Reason for this stricter rule obvious. As a (female) friend of mine says, men are the builders of (Islamic) nations. Women are the educators. But since most non-Islamic societies are patriarchal, a momin woman will be at a severe disadvantage, as will her children. The woman's rights will be affected; she will be expected to conform to non-Muslim norms; her children's social and moral education will be undeniably tarnished. An Islamic society is the best environment for a momin woman to serve her educational function to its fullest. Why else does the Quran call it an 'Ummah'?