I think the difference is in assessing a situation - is it always ok for all teens to drink? Or is it more about assessing whether to sometimes scare them a little by giving them a talking to and reminding them it’s not legal - and other times (if they endanger lives or get caught multiple times) enforcing the penalties as appropriate. Much like speeding or running a stop sign - sometime just getting pulled over is enough to remind you to slow down.
If they endanger lives, etc, we already have laws against that. If people regularly speed on a road the local government should consider raising the limit or installing speed bumps. If we have a problem with a law we should fix it rather than avoid enforcement.
