With all due respect, I, as a former active member of the LDS (Mormon) church must correct one of your statements regarding policy changes versus doctrinal changes. Discontinuing polygamy and black men being given the ability to hold the priesthood were absolutely NOT policy changes. They were direct changes to Mormon doctrine and those doctrinal changes were made due to political pressure. The change in polygamy was made for the purpose of allowing Utah to become a state (among a few other details such as relieving male members from being arrested and jailed) and the change in allowing the priesthood to be bestowed upon those of a "dark" race was made in the 1970's amid harsh public criticism for the bigotry that was being perpetrated within the church.
The idea that the Mormon church has never made any doctrinal changes is absolutely false. Along with that, I must take issue with one other statement you have made (not that these are the only two statements I take issue with, but for the sake of brevity I'm limiting myself). You say that "Gay couples cannot generate children, thereby making themselves an inherently limited family, rather than perpetual families..." I must ask if you've never seen a pregnant lesbian or a biological child of a gay man? If you haven't, you should acquaint yourself more broadly with the abilities of gay men and women being capable of producing their own children. At this point, I'm betting that your reply would be that the children of gay couples are not and cannot be the biological children of both partners and therefore cannot be considered "perpetual" families. The only problem with that logic is that it also stamps out the many families that have been sealed for eternity in a Mormon temple via the adoption process.
Your logic on that point would certainly be impossible to accept by the many thousands of LDS families that were created by the adoption of children by couples who were unable to biologically conceive their own. Painting the concept of same-sex marriage with this broad brushstroke is not only completely wrong, it's also horribly unkind and hurtful to say the least.
More information about text formats