Voting seems to be a materially unjust act, not a formally unjust one for most voters -- they have no control over who can be a candidate. In that respect, the parties and the "system" is at fault. Still, if they do not write in a candidate who they think is most qualified for the office, are they complicit in injustice? Who is an acceptable write-in candidates is determined by the state government, and I don't know if all states share the same rules. I am guessing that they don't. One can ask whether those rules or just or not, or if they place an undue burden on those seeking to exercise their vote in good conscience.