There is a joke, that helps people understand many of the issues here.
"God created Adam and Eve, not Adam and Steve."
If you believe in God, and/or the Bible, you may remember one of, if not the first commandment to Adam and Eve was to multiply and replenish the earth. It is biologically impossible for 2 men, or 2 women to "multiply".
Marriage just happens to be the means God has to unify each "Adam and Eve" with any children they have through the "multiplication" process.
Why would God, who created Adam and Eve, and instructed them to be married and multiply and replenish the earth, think it ok down the road for an Adam and Steve to be married, and not multiply and replenish the earth? Wouldn't that basically be those people saying to God, we dont like your plan, or think it is good enough. Isn't that also basically the same thing lucifer did.... I dont like your plan, I think it should go like this.... which got him where he is?
I think we should skip what our own agenda is and really ask ourselves, "What does God want".
Ask it honestly, and sincerely without thought for any ulterior motives.
Then, kneel down and in prayer, sincerely ask God if what you think he wants is really what he wants.
If you are honest with yourself, and honest with God, you will get an answer.
If you only want to defend yourself, someone else, or are on a crusade... you may not be open to an answer and will probably get nothing, and be in the same place you were before you started.
What is God's plan for us here?
Can you learn about God's plan from the Bible?
Can you learn about God's plan from the Book of Mormon?
Can you pray about these things and find out for yourself?
Are Prophets real? Was Joseph Smith a true Prophet? Is Thomas Monson a Prophet today?
Is the Church of Jesus Christ of Latter Day Saints the Lords true church?
If you actually go back to the basics and find out for yourself the answers to these things, it will help you resolve all of these issues discussed here in this thread. Many people with questions, or even arguments are wanting to argue point 10, when points 1-9 have not been agreed upon, or a common ground has not been reached. Difficult to reconcile differing viewpoints from different points on a map.