Salam 'alaykum... Why we are permitted to marry people of the Book while not permitted to marry deviant sects like Rafidha?

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 is His slave and Messenger.

Marrying the women of the People of the Book is permitted in Sharee'ah (Islamic Law). Allaah clarifies for us the women we are permitted to marry, saying (what means): {And [lawful in marriage are] chaste women from among the believers and chaste women from among those who were given the Scripture before you…} [Quran 5:5]

There is much wisdom in this, some of which has been mentioned in Fataawa 83101 and 87987.

However, Allaah has not permitted the believers to marry non-Muslim women other than the women of the People of the Book. Allaah says (what means): {And do not marry polytheistic women until they believe.} [Quran 2:221] Allaah also says (what means): {And hold not to marriage bonds with disbelieving women.} [Quran 60:10]

It is not permissible to marry those whose heresies amount to unbelief, such as those who believe that the Quran has been altered or that their Imaams know the unseen, are infallible or neither forget nor err; or those who seek help from the dead and pray to them beside Allaah or prostrate themselves to graves; or those who insult or blaspheme or pronounce as disbelievers the best humans after the Messengers and Prophets, the Companions of the Prophet .

Allaah Knows best.