Can the second "by" be omitted from the expression "not by (sth), but by (sth else)"?

Is it correct to omit the second "by" from the following sentences?

    This is not caused by evil, but by simple ignorance.
    ..., know that a person is not justified by the works of the law, but by faith in Jesus Christ.

If Conjunction Reduction rule also applies here, instead of saying "not by something but by something else", he could just say

    This is not caused by evil, but simple ignorance.
    ..., know that a person is not justified by the works of the law, but faith in Jesus Christ.