One justification for supporting Same-Sex Marriage for members of The Church of Jesus Christ of Latter-Day Saints is the argument from fallibility, Leaders of the church have declared that sex outside of a marriage between a man and a woman is sinful behavior. They have also encouraged members to support traditional marriage laws. Those members who support same-sex marriage will often use what might be called an argument from fallibility to justify their disagreement. The argument might look something like this:
P1: The Prophets and Apostles are mortal men
P2: Mortal men make mistakes
C1: Prophets and Apostles sometimes make mistakes
C2: Members of the church can support same-sex marriage and may be following God’s will in doing so (even from a ‘Mormon’ perspective), in spite of church leaders teachings to the contrary.
The response is that of course church leaders are fallible and can make mistakes. This fallibility can be seen as an ‘upper limit’ to where prophets and apostles might not be considered mortal any longer. Yet, if we believe these men are called of God there must be a ‘lower limit’ at which we might not consider them representatives of God at all.
There is a difference between some isolated statements by a few church leaders addressing a topic that is not a core belief, doctrine, or practice, and a consistent, unanimous message that is central to the restored gospel. And marriage between a man and a woman qualifies as the latter (see The Family: A Proclamation to the World). And topics like explanations for the priesthood ban, or something like Adam-God theories would be examples of the former.
There should be no mistake about where church leaders are on this issue. And faithful church members should not take their counsel lightly. On this, or other topics.
Eric Nielson
Small and Simple 
Yep, totally agree. I’m with God on the issue of same sex marriage. And He’s most certainly against it.
i stand against same sex marriage but I think the “consistent” point needs to be removed. On the doctrinal side, it was a consistent view for near 100 years that African Americans could not hold the priesthood. It was a consistent view for decades that women received their endowments only in special cases, marriage and missions. New revelation has also always brought change and new directions. We also see that things that were, are no more, and somethings that were and no more, are now again. So, I stand against same sex marriage, but I would be short sighted to say things there will never change. I have too much history from the days of Adam and Eve to the restoration and the last 50 years alone to teach me to know better than this is solid doctrine. Sometimes, you hear that we are to stick to true doctrine. I believe it will be easy to find, that a few first presidencies called the priesthood ban “true doctrine.” This first presidency does not refer to the priesthood ban as being so.
You make good points Richard. Yet I would add that the priesthood ban was always understood to be temporary. Even old Brigham Young said it was temporary. The other example of women and endowments seems to me to be the stuff of practice rather than doctrine.
By a unanimous message repeated over and over by Church leaders, you must mean something like the “doctrine” that blacks were not valiant in the premortal existence and therefore were not allowed to hold the priesthood. Or perhaps the repeated claims that polygamy produced superior children?
The examples that you give may have been common at a particular time, but I do not believe they were anywhere near unanimous, nor did they pass any particular test of time.