I will unequivocally state that it is abhorrent and terrible that an adult would have any type of sexually motivated interaction (kissing, petting, worse) with a teen, 'consensual' or not.
I will also say that I don't think that even a sin as egregious as that one, is unforgivable. I think that people can screw up, even that badly, and not be a waste of a human being. Not in all instances, but, I think there are indeed some.
I will give you an example. I was giving a rather charged opinion of a teacher who had a relationship with a student, and my husband stopped me. "I agree," he said, "a teacher has a sacred bond with a student that shouldn't be violated." Then he said something that I had already known, but, repeated in this context, sounded foreign. "My mother was 12 when she married my uncle. She was 14, when she married my father after he died. My father was probably around 50 when they married. My oldest sister wasn't 18 when she married. Half of my brothers' wives weren't 18 when they married. Not to even speculate on previous generations, but, my cousin's father was 94 when he was born...I'm guessing his mother wasn't. Does that mean that I come from a long lineage of victimized women and rapists?"
No, I don't think that it does.
While each country draws a legal line for what is, and is not acceptable...is that line so finite morally? I don't think it can be.
Don't get me wrong...if someone puts their hands on my daughter, I'm going to use them to rip out their heart. BUT, it gives me food for thought.