I was trying to say that the way you're outlining this issue about conscience is  one sided, and therefore it doesn't work.   

Just flip it over:   Can I argue that secular, pro choice people are denying the rights of conscience of prolife Catholics when they vote for pro choice candidates and policies?   

As Chaput wrote:

"Vatican II can never be invoked as an alibi for Catholics ignoring grave public evil or failing to act on their faith in the political sphere. That's a distortion of the council's message. It also misreads the U.S. Constitution. America's Founding Fathers did not say, and never intended, that religious faith should be excluded from civic debate. They intended one thing only: to prevent the establishment of an official state church. A purely secular interpretation of the "separation of church and state" would actually result in the "separation of state and morality." And that would be a catastrophe for real pluralism and the democratic process."