"This choice is freely made by those men who feel 'called' to the priesthood."
Therein lies the problem, 'men who feel' "called", rather than men who are called.
That's right. That's why they should seek out spiritual direction to help them find out if what they are 'feeling' is from God or not.
One 'discerns' the call before responding. The initial response is one of inquiry. The discernment process includes an understanding of the celibacy mandate. Ordination to the catholic priesthood is a lengthy process. Celibacy is only one part of "The Call".