Roadrunner,
I encourage you to state that you agree with SCOTUS. You cannot teach it as doctrine, but you could use it as an example of the fact that people have different opinions within the church. Besides the fact Elder Christopherson has said members will not be disciplined or impacted in any way for their opinion of same-sex marriage (so long as they do not attack the church), the letter itself recognizes the right of members to express opinions without retaliation: “The Church insists on its leaders’ and members’ right to express and advocate religious convictions on marriage, family, and morality free from retaliation or retribution.”
I say use this as an opportunity to show your ward its ok to have different political opinions. Belief in equal protection under the Constitution is not the same as saying something is moral.