Ex operato applies not only to the priest or bishop who is giving the sacraments, but to those receiving the sacraments. Remember, "from the act done", that the merits of the person receiving these sacraments is also part of this teaching from the Council of Trent. For a grace to be efficacious, that is, to work, the recipient must be in the right disposition.
A person either "in" mortal sin or "living in" mortal sin cannot receive sanctifying grace, period.
A "disposition" is not merely an attitude of mind, but a state of the soul. See all the posts I wrote below on baptism, confirmation, and marriage. This post is another attempt to contradict the never-ending story of false and poor catechesis among the laity. For more on this, see Summa theologiae, III, q. 69, a. 8.
We cannot wish a thing to be true. That is relativism. With regard to the sacraments, these are not merely signs, but "signum sacro sanctum efficax gratiae"--showing forth that which is hidden, and doing that which is signed. "Ex opere operato" does not mean that either the minister or the recipient must be entirely worthy, as that is impossible for all of us. Here is Leo XIII on the matter--"the Sacraments of the New Law, as sensible and efficient signs of invisible grace, ought both to signify the grace which they effect, and effect the grace which they signify" in Apostolicae Curae.
By the way, several months ago, I wrote about the author, Father Jordan Aumann, O.P. He is really good on these points. And, I just found his work online, a book which I have at home in a box! Here is the link. Please look him up when you have time.