Not at all.
Words are powerful, and the meanings we as a society assign to them are significant.
And both sides of this are concerned with the definition of a word. What does marriage mean?
If it means what Allie said it means (which is, I think it's fair to say, the common understanding of it), then same sex couples can't engage in it any more than a greyhounds can run in horse races, which is not a matter of unfair discrimination.
If marriage is something that is capable of including same-sex couples - in which case it seems fair for it to do so - then its definition must be something different.
In my opinion, this whole issue boils down to a struggle over the meaning of marriage. I think that establishing the possibility of same-sex marriage changes that meaning, and that this particular change is nontrivial, unprecedented, and should not be taken lightly.