That’s a good question.
I would say, that if someone isn’t a Catholic, there isn’t any moral obligation to call a priest “Father”, in a technical sense. It seems to me though, in a social setting it would be rather odd and awkward if one didnt.
For example, can you imagine the scene if one is in a group of people where a priest is present, and all are engaged in polite conversation. To address the preist in said conversation would be a bit awkward to say “Mister Thomas” when everyone else is calling him “Father Thomas”.
Similarly for an Imam (should anyone find oneself in the company of Muslims and their Imam).
So for the sake of a polite conversation I’d say it should be done. And perhaps that’s why it’s good this apologetic was posted. I would hope our non-Catholic brethren could put their mind at ease about this particular topic. Even if such do not want to become Catholic.
At least, one need not worry about calling a man “father”, regardless if a person is Catholic or not.
“Similarly for an Imam (should anyone find oneself in the company of Muslims and their Imam).”
I would politely excuse myself rather than eat with an Imam.
Avoiding social awkwardness seems to be “the easy way” of which we have been warned not to pursue. We are also properly admonished to make no oaths, none at all. I know that most would consider such a formality to be harmless, but God takes it very seriously, nevertheless.
I call most Christian ministers...”Reverend”. No one ever gets offended....though some of the more Pentacostal ones might have uttered a “pishaww” a time or two at the perceived ostentatiousness of the title! Baptists or pentacostals...I’ll often use “Pastor” as well as “reverend”....it seems to depend on the formality of the occaision.
I still call them by their last names only. Just wanted to see what some would post.