They got married because they love each other. When two people are in love, they don't see the skin color or their religion, but they see a good, loving, and caring person. Did you honestly think that ONLY Christians have good, loving, and caring characteristics?
St. Paul already gave you the answer (See 1 Corinthians 7:16-17).
1 Corinthians 7:15-17 But if the unbelieving depart, let him depart. A brother or a sister is not under bondage in such [cases]: but God hath called us to peace. For what knowest thou, O wife, whether thou shalt save [thy] husband? or how knowest thou, O man, whether thou shalt save [thy] wife? But as God hath distributed to every man, as the Lord hath called every one, so let him walk. And so ordain I in all churches.
We are to live in peace with unbelievers, not in hatred. God calls all people to know Him, but if the believer cannot bring their unbelieving spouse to know God and the unbelieving spouse departs, we are to let them go. They are to walk on their own to find God on their own or perish.
[/size][/font][/size][/font][/font]
So....the truth finally comes out. You see a non-Christian in the same level as a drug dealer and a prostitute, which is why you place them in the same category. How sad for you. When my aunt married her husband who was a non-Christian at the time, she did not see the color of his skin nor his religion. She saw a man who was compassionate, loving, caring, and an honest person. Of course, he had his faults like all of us, but she loved him even in his faults. Did she and her husband have problems with their different religion? Of course, they did, but they overcame those problems. In a marriage, that is what God expects us to do.....overcome the problems that always comes our way. And the person who puts God first is able to do that more easily because with God all things are possible.
I don't know about you, but God loves the drug dealer and the prostitute. We are all sinners. Do you think that you are better than them? It's ironic that you ask if a Christian should marry a prostitute. Did you not know that the prophet Hosea married a prostitute, and Hosea married her because he loved her (See Hosea 1:2). The prophet Hosea even wanted his prostitute wife to return to him despite the fact that she slept with so many men. This is the kind of love that God has for each one of us. No matter how many times we sinned, God still loves us.
One of my sisters in my community also prays everyday for her adulterous husband to return to her, and it's been 5 years since they separated. Now, that is what I call true love. Her husband betrayed her and is living with another woman, and instead of hatred and bitterness, she forgave her husband and prays for him and for the woman he's living with. She has learned to love the enemy. I must admit that I admire her for that because I don't think I can love the enemy let alone pray for them.