Celt, the basis of a straw argument relies on a misrepresentation of a position wherein that position is refuted by substitution, which does not really refute the original position.

In this particular case, the atheist's argument relies on a false premise by misrepresenting the "matter of choice" in conferring the Sacrament of Baptism on an infant. By substituting a proposition i.e. the absence of choice, the atheist creates an illusory position that the baptism is meaningless. Where does the refutation fail? The atheistic argument does not refute the theology behind the Sacrament thereby it does not render it meaningless. The argument relies on choice. But it still fails because, where the choice was not the infant's to make in the first place, neither would it have been of any faith community. It is a parental prerogative (whereupon the original position rests).