If you believe in this, you are a liar.
By saying this in response to gay marriage, you are explicitly saying you believe that the love they share between them is a sin against God and that it should be torn apart, ripped asunder. It is unequal, it is lesser, and they are less human because of it. Using mistranslations and re-translations (don't think that everyone has forgotten that American protestants changed the wording of the bible for the sake of politics) to justify hate is nothing but an attempt to defecate on Jesus' message.
I am not as gentle as others are about this topic-- nor do I claim to be. Actively hurting people because you call them sinful is, itself, a sin against God. As is preferring children to starve than to associate with "sinners"-- if there are fiery pits of hell like many such bible-thumpers believe in, then that is a sin explicitly stated in the bible that you will be thrown in to it for committing. Lying is also a sin, ESPECIALLY lying in order to hurt people-- which is something that bible-thumpers love to do. Reducing people to nothing but their sex drive is nothing but hate as well.
Love though, is not a sin. Be it the gentle, playful love of a close-knit family, the passionate love of newlyweds, or the everlasting love of lifelong partners, love is the opposite of sin. Love is, in fact, God.
There is too much pain and suffering in this world. Stop spreading more...