Remember that Baptism is a Sacrament, the only one that can be given even by laity.
The efficatiousness of it, does not depend on the person administering it.
Even someone being Baptized by an atheist will receive a valid one, as long as the proper formula is used as taught by Jesus.
This is why the Church recognizes as valid the Baptism of many protestants traditions, even when many do not believe in the Sacramental aspect of it and yet since they preserve the proper form it remains valid.
We as Catholics however are also bound by the law of the Church, (the Code of Canon law) therefore should respect what She requires for the Sacrament.
We as Catholics would only be allowed to perform the Sacrament in extreme circumstances like life and death situations and a Priest not been available.