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Does the government have a right to create a law which will take away a person's freedom without first proving that person has committed any crime?
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Governments have no rights. And they don't have the right to restrict people's freedom*.
*There is no freedom to kill people who aren't a direct threat to you or someone else.
Basically, your scenario is a more complicated Violinist Dilemma. For a refutation of said dilemma, check out
this article.