Honestly, this whole thread is easily answered in one simple statement, both sides.
If you believe in the Bible, follow the Bible. Namely, the Torah. It outlines pretty much every single possible scenario of sin, how to avoid it, and how to solve it. It defines sin, and gives us a general standing stone for what we need to know about the definition of sin. It really shouldn't be that hard to figure out to be honest... We make it harder than it is.
However, for Atheists and those who do not subscribe to the words written in the Scripitures, then things are a little more cloudy. Yes, you can define what is 'good' and 'bad' or 'right' and 'wrong' based on your moral compass. However, that compass can be skewed quite often, towards one extreme or the other. If you don't necessarily have a set of guidelines for what is right and what is wrong, then it is difficult to peg an individual as guilty of something. I mean, think about this James Holmes guy. He obviously was in the wrong when he murdered so many people (hits close to home because I know people that were in that theater room, it was 10 miles from my house). However, if you don't have a set group of rulings, statutes, and laws, how are you to convict someone if what's right to them is just okay? Sure, you can argue that if everyone thought that what Holmes did was okay, then he'd be let free. That is true. However, if that were the case, none of us would still be alive because we'd all be at each others' throats. Post-modernism sounds nice, in a sense. You know, I can understand that. However, at the end of the day, it's a utopian mindset, it doesn't exist in a fully-fleshed out system. If everyone was naturally good then it would be okay. However, by nature, man strives with man. We are not good, and it's obvious. If we were naturally good, then post-modernism would work perfectly because we would all generally adhere to the same ideas. But we don't.
That's the main problem I see with following a more cloud-based system of self-governing.