“I am not saying that no ex-priest or ex-nun should ever be employed as a teacher.”
This was indeed the case pre-Vatican II.
It might have seemed rather harsh – but I suspect that the reasons for it were as follows:
- To avoid sending mixed messages to children. A priest makes promises for life – like a married couple.
- Some (not all) former priests and nuns may disagree with the Magisterium on some matters of faith or morals.
- Some (not all) former priests and nuns may have lost their faith.
Nowadays (so I am told by those who are more knowledgeable than me) former priests and nuns may become teachers at a Catholic School – on a case by case basis.
But obviously great prudence and care is needed to avoid scandalising children.
Sadly I suspect great prudence and care are not always taken.