Your friend is probably confused by the fact that God seemed to act directly with Sodom and Gomorrah, destroying both cities in dramatic fashion, those people KNEW it was coming from God too, versus todays world with plenty of cities where sexual sin is plentiful…yet God does not destroy them…Heck, they dont even get warnings!??
Ive heard many people ask this type of question, many claim this is one reason they dont believe the bible, as if God did that back then, why would he not do the same today, that leads them to believe the bible is fiction.
I dont know the answer, the only I can think of is it may a time issue, Im not sure how long the sin went on in those biblical cities before God finally said enough is enough, it could have been 100s of years, if you look at our modern world, sexual immorality has really only gone off the charts fairly recently (when you look at the big picture).