So out of context and not pertinent.
That is the exact context - obeying the law. The theme of the entire chapter is the Christian duty to obey the law and consequences for not doing so. Paul is saying God establishes governments and they do not wield the sword for nothing. We know what punishment a sword is used for.
Why is it "out of context" for a conservative American to consult the Bible for guidance on moral issues, such as whether capital punishment is justifiable?