I think I'd need several sessions to get anywhere, honestly. I think I'd try to demonstrate that many people, at least where I live, don't actually know nor have ever wondered what they believe in, what their values are, what point there is to their lives besides hedonism and consumerism (might as well die if your life is that vacuous, NGL) and whether they even believe in objective truths and right and wrongs. Instead of a regular PSA, I'd make a live interview with random members of the crowd. And finally I'd tell them that all their social issues, all the issues regarding the distribution of resources, their misogyny, their love of imperialism, the reason they're not raising families, etc etc are born from this ideological vacuum (and that comes with a lack of a moral framework, ofc). And I'd tell them it's their duty to live like humans, not beasts, and not to be surprised if they end up in hell (they don't believe in it but still, and I'd comment on that and say it's part of it, because acknowledging a day of Judgment would imply personal responsibility) if they keep acting this way, they've been warned again and again.