where in the bible does it prohibit butt sex between married couples?
I really don't know why i have to respond to this and in fact it scares me to think you actually accept it and probably do it. Well then again i have read some of your stuff and sorry to say but you are really not a true Christian but are being mislead by your own desires in life which blinds you from the truth, you choose to hold on to both worlds as you do not wish to give up what you love so much in the world of mankind. In this matter one does not even need to quote a text to know by heart it is wrong! It is not a natural way, and if think it is then you really are sick.
Sodom and Gomorrah indulged in sexual immorality and pursued unnatural desires and their penalty was death and so will those receive death to any who act in this fashion. Homosexuals commit sodomy and so is it an abomination to do the same with a women.
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Therefore God gave them up in the lusts of their hearts to impurity, to the dishonoring of their bodies among themselves, because they exchanged the truth about God for a lie and worshiped and served the creature rather than the Creator, who is blessed forever! Amen.
For this reason God gave them up to dishonorable passions. For their women exchanged natural relations for those that are contrary to nature; and the men likewise gave up natural relations with women and were consumed with passion for one another, men committing shameless acts with men and receiving in themselves the due penalty for their error.
And since they did not see fit to acknowledge God, God gave them up to a debased mind to do what ought not to be done. They were filled with all manner of unrighteousness, evil, covetousness, malice. They are full of envy, murder, strife, deceit, maliciousness. They are gossips, slanderers, haters of God, insolent, haughty, boastful, inventors of evil, disobedient to parents, foolish, faithless, heartless, ruthless. Though they know God's righteous decree that those who practice such things deserve to die, they not only do them but give approval to those who practice them.
[Romans 1:24-33]
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If you cannot see that such an act is sexually immoral then it shows how far you are from God and how close you are to the worlds heinous desires.