You do realize that the diaconate is part of the Sacrament of Holy Orders, don’t you?
Step One: Diaconate
Step Two: Priesthood
Step Three: Eposcpate (Bishop)_
No slippery slope about it — if the wife of a deacon dies, he cannot remarry. So if he does wish, at that time, he could go back to school and become a priest and remain celibate for the rest of his life.
Is the celibacy what you are worried about?
My original post stands.