I know that I would not want to marry someone and then find out that they were not attracted to me physically.
I don't think it's a sin to not find someone attractive. But if the absence (or presence) of good looks causes someone to look down on someone else or treat them poorly, then that's when it becomes wrong.
I don't think it's a sin to not find someone attractive. But if the absence (or presence) of good looks causes someone to look down on someone else or treat them poorly, then that's when it becomes wrong.