Whether is be the pot-smoker or the gun-owner, there are those on one end of the spectrum that are responsible users and those on the other end that are irresponsible.
Therefore, it is easier to legislate against the object than the person, so government just makes "the thing" illegal, effectively punishing the responsible in order to affect the irresponsible.
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Pastor Martin Niemöller still applies...
First they regulated machine gun owners, but I was not a machine gun owner so I did not speak out.
Then they regulated marijuana smokers, but I was not a marijuana smoker so I did not speak out...