Did ‘Umar, may Allaah be pleased with him, divorce his Christian wife because she did not accept Islam? If yes, then why is this not mentioned to our brothers who abuse and distort the fact that Muslim men can marry chaste women of the book?

All perfect praise be to Allaah, The Lord of the Worlds.  I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

There is no evidence that ‘Umar married a Christian woman at all. So, saying he divorced his Christian wife because she did not become Muslim is wrong. On the other hand, it is lawful for Muslims to marry Christian or Jewish women, provided they are chaste. Allaah The Almighty Says (what means): {Made lawful to you this day are At-Tayyibaat [all kinds of Halaal (lawful) foods, which Allaah has made lawful (meat of slaughtered eatable animals, etc., milk products, fats, vegetables and fruits, etc.). The food (slaughtered cattle, eatable animals, etc.) of the people of the Scripture (Jews and Christians) is lawful to you and yours is lawful to them. (Lawful to you in marriage) are chaste women from the believers and chaste women from those who were given the Scripture (Jews and Christians) before your time, when you have given their due Mahr (bridal money given by the husband to his wife at the time of marriage), desiring chastity (i.e. taking them in legal wedlock) not committing illegal sexual intercourse, nor taking them as girl-friends…}[Quran, 5:5]

If the Christian or Jewish woman is in a country which states in its laws that the children should follow their mother's religion, then it becomes prohibited to marry them to avoid causing a much greater perversion. This is not contradictory to Quran. It is actually conforms to all the principles of Sharee’ah (Islamic law).

Allaah Knows best.