I've heard that argument made my several readers as well. They don't bother to mention all the ways gay people continue to be discriminated against, not just socially, but by the law itself.
They can still be fired for being gay in many states, as well as kicked out of housing.
People still openly and hostilely preach from pulpits that they are not just sinful but abominations in the eyes of God.
They face higher rates of suicide because of the stress that comes with being a put-upon minority.
They still face assaults of various kinds because they are gay.
And in the vast majority of states, their unions are not only not recognized legally but are frowned upon. If a gay person puts a picture of his loved one on his desk, he is flaunting his sexuality. If a straight man does the same, he is just honoring his wife.
If gay advocates were so powerful, why are they still not treated equally before the law?