If a dedicated servant of Jehovah married an unbeliever, this would be an act of disobedience to God. The Israelites of Ezra’s day acted unfaithfully by giving “a dwelling to foreign wives,” and it would be wrong to try to water down the plain statements of the Scriptures. (Ezra 10:10; 2 Cor. 6:14, 15) A Christian who marries an unbeliever is not exemplary and lacks real appreciation for God’s gift of marriage. Entering such a union after baptism can cost one some privileges among God’s people. And it would be illogical to expect blessings while admitting in prayer, ‘Jehovah, I deliberately disobeyed you, but please bless me anyway.’
This is really offensive considering all of the single people in the religion, especially women, who because of the WT's self serving interpretation of "marry only in the Lord", as well as "all scripture is inspired of God", untold thousands if not millions are single without any chance of ever getting a partner. What really adds insult to injury is the WT encourages them to simply peddle more literature, pioneer, study more, as if that's the one pill solution to all of life's problems.
I love how the apostle Paul's words trump the Lord's by the way. The chapter in Corinthians where the WT points out to "marry only in the Lord", also contains Paul stating that the advice he gives is that of his own, not the Lord. (1 Cor 7:12) By the way the material support they use to bring gravity to situations of marriages between JWs to nonJWs, namely the examples of those living in Ezra's day, is a moot point. We're not living in Ezra's day, and we're not under the Mosaic Law. Heck, if you really want to get technical about it, WT doctrine stipulates that we're not even part of Spiritual Israel, so why should it even matter if the average non-annointed JW marries a nonJW?
One last thing, if a JW gets involved in a relationship with a nonJW, they're not disobeying God, they're simply not following the apostle Paul's advice.