Just another twist on this... and it's only my own two cents, but Jesus said that anyone who looks at another person with lust in their heart has already committed adultery with that person in their heart.
I could be misunderstanding, but committing adultery, even in the heart, would make one an adulterer.
By that definition, how many people would be able to say they are non-adulterers or have never committed the sin of adultery?
I'm sure there are a few who have never looked at someone or images on TV, in magazines, movies, etc. with any lustful thoughts, but I would guess they would be pretty hard to find.
And if that's the case... it would mean only what... five people in the world would be free from every committing adultery, whether in body or in mind, and would, therefore, be free to marry? (So sorry for the fifth person... they obviously would not be able to marry by the default of the odd numbers!)
So, my answer would be... show me two people who are absolutely, 100% free of any adulterous or lustful thoughts, and by all means, we've found two people who are so nearly perfect, they certainly qualify to marry.
*Sits and waits. And waits, and waits, and waits...*
Just my own take is all.