I'm tempted at this point to ask which is essential for a Christian viewpoint: to believe that murder is wrong, or to believe that we can be philosophically certain that murder is wrong?
I guess I'd have to say it depends on the level of knowledge one has. One can be a very simple, unsophisticated believer (a farmboy, to use the Reformation-era example) and believe that he has done bad things and that Jesus alone can save him from them, and God saves him. Or one can be a super-prof of theology and be responsible for much, much more. One can be a sorta-well-read layman who struggles against pride, like me, and be responsible for quite a bit as well - what to do with the knowledge I have, how to understand it, and what not to reject when I'm corrected. So I'd say for me, I couldn't in good conscience reject either proposition. But start removing education and intellectual prowess (not that I have a lot to begin with), and somewhere in there (God knows where) it's simply enough to believe murder is wrong, and perhaps even further, our simple farmboy might not have ever even thought about it. But we trust the Holy Spirit to make that good in the life of the believer, from the simplest to the most erudite, and thank God.