I'll assume you are invoking the Romans 14 (v4 et al) passage here, and if so, I think it relevant that in the same way that you'd make application of not being judgmental, you'd also have to concede that the spite which you seem to demonstrate is forbidden ("do not despise him that eateth"...v3), because not all realms of judgment which result in differences of opinion come from phraisees/legalists nor do the opposing side's viewpoint necessarily constitute antinomian ideals.
If a young person thinks that it is inappropriate to consider the implications of their behavior, and the risks that might arise from said risky behavior, then I'd leave them to their own conscience and consequent outcomes. You can lead a horse to water, and all that.