I believe they can however, at least in theory, get you for perjury if you tell them that you that you would only use the letter of the law to determine innocen

I believe they can however, at least in theory, get you for perjury if you tell them that you that you would only use the letter of the law to determine innocence or guilt but in fact are aware that you are not required to and are willing to not. It is unfortunately likely that I will never serve on a jury because 1) I would never convict somebody of a crime if I believe that the law is unethical, and 2) would never lie about that.