Conscience can be and is formed within the Protestant world by the Gospels and by their theologians meditating on and expounding issues of conscience.
Seeing as we have less than a month left in this forum let’s see if we can make it productive. I don’t think that the Gospels, or the Catechism, or theologians are the source of a well-formed conscience. I think that anyone, anywhere, can have their own inner sense of what’s right and what’s wrong. This doesn’t mean that everyone will love their neighbor as themselves, but it does mean that anyone, anywhere, has the capacity to recognize the virtue in that sentiment, and to live by it. Neither does it mean that they will, it simply means that they can. And it has nothing to do with whether or not they’re a Catholic.
The atheist’s conscience can guide them just as altruistically as a Catholic’s can. It may not be as codified as yours, but that doesn’t mean that it’s inferior to yours. Even someone without the law, can do by nature the things contained within the law, and we call such obedience a conscience.
A well-formed conscience isn’t just a Catholic thing. Now you may choose to use the Gospels, and the Catechism, and theologians as a guide, but there’s something to be said for that still small voice, unless you believe that Catholics have a monopoly on that as well.
I have a conscience…and because I do…I am not a Catholic.