Why does the government really care if people sell or use drugs?

I mean, it's not like the government cares whether citizens live or die, and it's often instrumental in killing citizens and it is also instrumental in killing citizens themselves. So what difference does it make if somebody deals some drugs and uses some drugs or doesn't? Who cares If the government makes a big deal out of it - why?

Why does the government really care if people sell or use drugs?
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