I lived in the Middle East for three years and although some Muslims did try to interest me in Islam, none of them told me to my face that I was damned because I wasn’t Muslim.
I’ve worked with plenty of Muslims and so has my husband and many other people we know. I also live in a city that has had a lot of Muslims emigrate to there. While the vast majority of them are polite and would not say such things to strangers, work acquaintances, neighbors, etc. you can get a very different picture if it’s actually a case of their son wants to marry a Christian or whatever. That is why I think the whole scenario posted by the OP is some type of a parental, family or close friend affair.
In some parts of the Middle East, and I stress “some”, you will get a lot more anti-Christian sentiment. Other places people live in peace.
I also had Baptist relatives in my father’s family who were not happy about him marrying my Catholic mom. I was too young to know they disapproved, but my mom had to put up with it. Also, my dad’s Methodist father would have likely thrown a fit but fortunately he had died before Dad met Mom. My dad’s father was in the KKK as were quite a few people from his area, and it was primarily an anti-Catholic organization out there as there were few or no Jewish people or people of color but there were a sizable number of Catholics around.
The bottom line is we all have to put up with disapproval sometimes, and it very rarely comes from a total stranger.
The OP has chosen to present a situation with no context, making it sound like this Catholic person just walks up to random gay or trans folks on the street and starts “scolding” them. I sincerely doubt that’s what’s going on here. I’m not even convinced this is all about “my best friend” because half the time when people say “my friend” they mean themselves.
Leaving the thread now, have a nice day