@Madhatter,
1. Marriage is not DEFINED as being fundamental to our very survival, it is simply DESCRIBED as such in a court decision.
2. You seem to want to overlook the part of the decision that clearly states that is is a RIGHT. You are not talking to children, so when you switch the word RIGHT out with PRIVILEGE, you're not fooling anyone.
3. You have failed to provide an answer to the question of a married man who gets a visectomy.
4. You have failed to provide an answer to the question of a heterosexual fertile individual who chooses to marry a heterosexual sterile individual. (and before you fire back with that "behavioral" non-sense, please understand that a heterosexual, fertile individual is making a CHOICE to marry someone who cannot have children.)
5. Why hasn't anyone, even a religious person... even another LDS member... come to the defense of your argument with secular reasoning?
You need to simply understand that you have lost the debate. I'm sure that 95% of forum members would agree with that assertion.