I don't think he is saying that there isn't absolute good and evil. He's saying that everyone's compass doesn't measure the same.
You see it in the New Testament. Some were offended by eating meat that had been offered to idols. Other knew the idols weren't real and that meat was meat.
You see it today among denominations. Some feel drinking is a sin. Others recognize drinking in moderation is okay.
And in some cases there are ligitimate differences in conscience that do not arise differences in understanding scripture.
What may be okay for one person is not for another because God has told that person not to do something. And the inverse could be true to. God could have commanded someone to do something, so it's a sin if they don't do it, but God didn't command that same thing of others.
the problem is the vague language. “as he conceives them” — due to what? due to the direction of God (that’s great) or due to some unknown factor (that’s asking for big trouble)?