The statement "Who cares?" is often seen as extremely rude and even arrogant. Let's look at a more specific case: consider George W. Bush's response to journalist Bill Hangley at a press event in 2001:
Because I had serious misgivings about the president’s performance to that point, my own involvement in the whole operation had left me feeling a bit like a pseudo person, so when I had the chance to shake Bush’s hand, I said, “Mr. President, I hope you only serve one term. I’m very disappointed in your work so far.”
His smiling response was swift: “Who cares what you think?”
This is a very small thing for a man in a position of importance to say. Although Hangley had criticized the president to his face, a man who was more sure of himself might have replied generously, even magnanimously: "I'm sorry you feel that way," perhaps, or "I am doing my best to change your mind." That sort of thing. Instead, what came out was rude to the point of arrogance. It is the statement of someone in power to someone who is powerless.
Granted, "Who cares what you think?" is more specific and pointed, but the general "Who cares?" amounts to the same thing.
But the statement is not always rude. It may also be a weak response to an accusation:
A: You know smoking will kill you, right? Yet you do it anyway.
B: Who cares? We all have to die of something.
That usage suggests a forced insouciance, a resignation in the face of the perceived powerlessness of the person to quit smoking.
It can also be triumphant and expansive, even exultant in a way that is not at all rude:
A: The weather report is saying heavy snow is expected next week.
B: Who cares? You and I will be at the conference in Hawaii that week!
Best Answer
The word Systemically would cover the entire body and its subsystems. In your example, you could say, "Drugs are systemically bad," or "Drugs are a systemic problem."