I'm not sure I'm the best one to be arguing this position but I can give it a shot I suppose...
I lean towards the first part of Socrates' question... Things are good inherently, not just because God says so.. I think that sins are declared by God because he has his own judicial system for good and evil. And from Romans 6:23 we know, "For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord."
But even in the beginning, there was only good on earth.. and yet God made the tree of the knowledge of good and evil.. So there was knowledge of good and evil that God already had but we didn't.. until Adam and Eve ate from the tree and then they were made aware of evil..
There are a lot of weird and funny laws in the old testament that are really just for that time period.. whether it be for hygiene purposes or certain rituals that are no longer required of us because of Jesus' death on the Cross... so I'm going to ignore those ones to discuss and focus on ones still relevant today..
I'll go through the 10 Commandments and tell you all the natural consequences I can think of for each.
1)
You shall have no other gods before me. - when you worship more than one god, which god trumps the other if they have 2 different views on things? It's like with parents, if one says no and you go and ask the other and they say yes, it's dishonest.. and hurts everyone in the situation...
2)
Not allowed to have idols - for one thing, when you idolize things or people, it takes up your time and your energy and most of the time idols give nothing back to you.. So you waste your money and your time for nothing..
3)
Can't misuse the name of God - when you say things like "oh my God" or "for Christ's sake" it's like swearing, and it changes you with repeated use.. At least in my own experience, if I'm careful with what I say, I don't hurt or offend people, and I'm just a better person..
4)
Remember the Sabbath day by keeping it holy - If you look at America vs. countries that actually VALUE their days off, it is like night and day... In North America we continue to increase our numbers of stress-related illnesses and life-threatening issues (blood pressure, heart attacks, etc.) .. It's important to rest. It's important to have days that you don't work so that you can enjoy life..
5)
Honor your father and mother - My parents love this one... I work with kids all the time that have no discipline at home.. and they don't listen to their parents, so why would they ever respect their teachers? or in the future, their bosses? .. Respecting your parents and doing what they say trains you to get through life.. It ALSO protects you from dying or injuries when you're a kid.. "don't use the knife like that, you'll cut your hand off" or "don't touch the stove, it's hot" .. or whatever..
6)
You shall not murder - well that's obvious, if murder was okay, life would be chaos.. Murder changes the murderer too... unless they are a sociopath..
7)
You shall not commit adultery - Obviously adultery in marriage is devastating to the marriage.. creating trust issues, insecurity, anger, resentment, etc... but even to extend this to all forms of sex outside of marriage... how do you think STDs were created? God designed sex for a man and a woman who were married... if every single person on earth from the beginning of time honoured God's design for sex, we would not have STDs or pregnancies outside of committed relationships.. Not as scary with 2 people.. Unless you're having sextuplets or something
haha..
8)
You shall not steal - It hurts others.. it could be something they really cared about or worked really hard for.. If you get caught, it's embarrassing and could possibly mean you lose your job or your computer, or other things, depending on what you stole.. if you steal money or information you could go to jail...
9)
You shall not give false testimony (lie) - another thing you could go to jail for, depending on where you lie.. if you lie to your partner or your family it causes trust issues, and hurt feelings and resentment..
10)
You shall not covet your neighbor's possessions - This one I think of more as greed.. or continuing to want what you don't have.. It's just a miserable way to live.. To always strive for something and never be happy with what you have.. if it's family - they feel that, if it's money - you're never going to have enough, etc.. You're just never going to be happy with your life and you will be a miserable person to be around.. like those people that are always complaining about everything.. the other thing is, if you continue to dwell on it, (in extreme cases) it can drive you to do things you shouldn't do... like steal or murder..
So to sum up.. Thinking totally outside of God's plan and how he feels about sin... Sin in itself is bad.. There are consequences outside of God's consequences that prove that..
But then there's the question, is sin the absence of good? and is evil the absence of God? and then my head starts to hurt.... someone else can try that one!