The problem with stressing a point is when it involves extreme exaggeration. Kids who go mamesh OTD (meaning they are no longer Shomer Shabbos, kosher, possibly into drugs or alcohol, though not necessarily) often get disillusioned by hearing stories about such extreme behavior as was described. To them (and to me, I must admit) it is not praiseworthy that someone would consider jumping off a train and possibly killing himself, because he was in yichud with his own kallah. IMO it would have been more praiseworthy had he looked for a way to avoid the situation l’chatchilah, but given that he could not, to show that he is a trustworthy frum person even under this type of duress. Were there no other cars on the train? There surely was a conductor or engineer, so was he really in yichud?
My point is that you don’t impress kids who are already religiously in crisis, by telling them these types of maises. they go OTD because they feel disenfranchised, and do not care for the fact that they are thrown away. There are rabbonim and lay people who work with such kids with great success. They are patient, loving, and welcoming, not stern, judgmental and dismssive.