It is an Islamic matter and I really don’t like to talk with non-Muslims (especially Hindus who are biased towards Islam by default) who do not have slightest clue of what they are talking about. By the same token, I dont like to put my nose in any other religion. But just to clarify another misconception here;
It is not purely political, it is not political at all. In Islam, the major purpose of marriage is the procreation of the offspring. Islam is a monotheist religion (like Judaism and Christianity). In Islam, every sin is forgivable except worshiping of more than one God. Monotheism or Tawhid is the foundation of Islam.
"Verily God forgives not setting up partners in worship with Him. But He forgives whom He pleases, sins other than that (shirk)" The Holy Qur'an, Chapter 4, Verse 116
"Verily whosoever sets up partners in worship with God, then God Has forbidden paradise for him and the fire will be his abode" The Holy Qur'an, Chapter 5, Verse 72
"And invoke not besides Allah any that will neither profit you nor hurt you, but if (in case) you did so, you shall certainly be one of the polytheists and wrong doers. And if Allah touches you with hurt, there is none who can remove it but He; and if He intends any good for you, there is none who can repel His favours which He causes it to reach whomsoever of His slaves He wills. And He is the Oft-Forgiving, Most Merciful" The Holy Qur'an, Chapter 10, Verses 106-107
It is well understood that a mother is the first learning institution of a child. If Muslims were allowed to marry with women from Polytheist religion, it would be counter productive for a Muslim child who would now get his first information on religion from a polytheist mother. In addition to that, there are all kinds of social problems associated with these marriages. That is why it is best to marry with a Muslim woman, than with the women of other monotheist religions.