I believe it's important for everybody to be informed on the big picture before casting judgement on anybody.
Understanding the common nature of coke use in nightlife is important when looking at this case if you'd like to get past basic duality in your view of things. Just because you consider yourself healthy, does not mean that you are a perfect person in every other aspect of your life. Perhaps there is an area of your life where you are making equally poor decisions, and you look the other way because it is commonplace (lying, selfishness, etc.). Not accusing you of any of these, but giving you a thought experiment since everybody has a vice. Are you really a better person than Chung because you don't do drugs? Is there anything you do that's immature for your age?
Socially acceptable is not equal to ethical. Those are two different arguments.