People do not always arrive at decisions instantly, especially if they begin a position in good faith and then like a boiled frog find themselves in an untenable position because the government and political milieu have changed around them.
Yes, you are a better person if you would have instantly known to not send the letters. You are a more perfect person if you would have always known that.
However, with regard to logic and statements, it is flat-out wrong and simplistic binary thinking to say "resigning after you did their bidding isn't showing you have a conscience".
First, "conscience" is not pure, is not all-or-nothing. People can have good conscience without being saints.
Second, when a person arrives at a conscientious point, they have crossed a threshold. Perhaps you have always had a good or perfect conscience, but few people are like that. Most people have to work things out, especially when things don't turn out the way they expected. I doubt Wilson ever expected to be placed in the position of being ordered to violate the First Amendment.
A person who develops a conscience or expands their conscience is NOT a 'person without a conscience'.
Nor do you know Wilson's situation. For all you or I know, he might have dependent children needing lots of medical treatment that he would lose by resigning. Or perhaps he was threatened with "You will never work in law again if you don't send those letters. We manufactured some damning evidence of financial fraud we can use."