It is charity.
There is a grave absense of charity in our world today, especially amongst those (Christians) who should be living charity with every breath, and I certainly include myself.
Oh, perhaps, objectively speaking, we have a right to condemn the sin (you know, as in condemn the sin but love the sinner) but it seems there is a terrible imbalance, an awful lot more of condemning the sin and not enough (by far) of loving the sinner.
And when we do all the "condemning the sin" that we do, we are in fact, implicitly condemning the sinner as well.
True charity, faithfully, consistently lived out, is the only argument that will convince. In the end, most who end up embracing the true God will do so because one way or another they witnessed the great love of God, and most of the time, through the faithful consistent living out of Charity by Christians.