If you could turn back a tide and make it so marriage equality would fail entirely I could see the argument.
But there are two certainties in play here.
1) You, and I and everyone else will die someday. And you (and I) sooner than most.
2) Same sex marriage will be generally accepted a generation from now.
If you accept the truth of those two things... what are you doing? You are merely messing with young people out of spite. Young people today, at the age when most people form these sort of bonds, think same sex marriage is okay.
The age group that is actually getting married in large numbers wishes their gay friends had the same right.
Why seek to dictate your will to them on a matter of great practical importance to them and lesser and lesser practical import to you? That would be like an elderly man who had never had sex in his life dictating policies on birth control... oh, right. The Pope. Okay, bad example... but, I mean c'mon... it's not like older people have ever supported a war that young people opposed and that young people would be forced to fight to serve your whims... okay, that's another bad example. But you get the point.
All you are doing is saying to some young person, I want to live out what remains of my life knowing that I am preventing YOU from getting married... not gay people in general, just YOU, here in 2013, even though people a few years younger than you will be able to get married without incident or controversy. It seems very personal...
If you just want to steal something from the next generation, why not steal their ability to be the generation that made marriage equality universal by beating them to the punch?