Yes it has, and the generations coming to power over the next few decades are not on your side. I don't think you're going to succeed in convincing many young people who now think it is ok to change their mind in their 30s and 40s.
In the 1920s there were more Laissez faire attitudes about sex within a few short generations that changed. The same has occurred many times over the past 1000 years. People do change their minds as they grow older and start having children and become more sexually conservative. Wide spread norming of pornography, the politicizing of sex and the thought police element of gay activism as well as active academic suppression of anything not kosher to gay propaganda has led to what we see today. There will be greater and greater opportunity for backlash, even in France and the UK there has been a large backlash even though it was assumed SSM was no big deal in those long progressive European bastions. Also when the negative consequences of the thought police continue to grow attitudes will change. Gay marriage is not for the youth an issue they view as critical. They may feel its no big deal but when they are educated to the otherside they often change their mind. It worked in prop 8 and even though in 2012 things did not work out as well in blue states with high Democrat turnout the traditional marriage vote exceeded the vote given to the GOP Pres candidate by a large margin.
This issue is not going away. There is an ebb and flow and right now we are in a good position with the gay activists and left overplaying their hand. Eventually we will get the perfect victim of gay political correctness and minds will be changed like the case below.
http://www.youtube.com/watch?v=unhly6XNtck&list=UUd0zHbtp58-vfdaqG6klBCg&index=1
When abortion was legalized 40 years ago the libs thought the same thing — they had won and the younger generation was on their side. But a funny thing happened as time marched on. The younger generation now sees abortion as taking a life and is not so willing to support it any more.
Anyone who imagines the gay marriage battle is already lost has no idea who is leading the fight and that He won the war nearly 2000 years ago. Unless you are already standing on the losing, pro gay marriage side, you have no reason to give up.