I think if you remove the objective standard of God, a case could be made for a lot different morals.
If your enemy is ruining your life, is the only thing stopping you from murdering them that it's against the law? If you feel there is a deeper truth involved stopping you, what is that basis?
And why don't you pay for prostitutes if you are horny? I often tell people, if it wasn't for my Christian faith, I'd frequent sex workers a whole lot more. Is the idea that you feel you're exploiting them so don't do it? I think a basis could be made sometimes that it's not exploitation, but even if it was... why would you care?
It's an interesting series of questions that you pose here. Thanks.
You are correct that without a set of objective standards, then anything goes. Standards will become the domain of the powerful, the rich, or in the case of most of the West, the majority. The question that needs to be addressed is "Who will decide what is right and wrong"?
In the case of murder, there are plenty of reasons not to do so. Yet, the fact it is against the law and attracts severe penalties is a huge reason not to do so. Of course not doing so, doesn't mean that most people don't dream of doing so, or would like to do so if they could get away with it.
Concerning prostitutes, it's not against the law in most countries. It's a question of morality and faithfulness. Exploitation tends to go both ways. Yes, it exploits people if you use them. On the other hand, many people enjoy the work and believe it is their legal and legitimate right to use whatever resources they have to make a living.
As to the question of people's goodness or badness, this is a vexed question. How people understand the essence of humanity, whether individual or corporate is varied. Take individuals like Einstein Hitler or Trump or Swaggart or Hawking. Each of them would probably say that humanity as a whole has good people and bad people. Each would probably say that sometimes "groups" of people are worse than others. Yet NONE of them would hold to the idea that they as individuals are bad. They might say that any of the others on this list are bad. But how do they determine this value and how do they measure it?
The Bible talks about humans pre-Fall. It talks about them post-fall. It talks about them post-Christ. And it talks about them in eternity. Pre-Fall, humans were good. After the Fall, ALL people were sinners. Post-Christ, ALL people remained sinners, but some were no longer slaves to sin. In eternity, those who inherit life with God no longer sin and are perfect or holy. And those who don't inherit life become everything their heart desires per their slavery to sin.
The doctrine of Original Sin, which many people reject or redefine depending upon your unique brand of Christianity, is the primary teaching of the Church. It teaches that people are born into sin. This was passed down to each individual from Adam. In Reformed circles (My unique brand of Christianity) we call this doctrine the doctrine of Total Depravity.
Total Depravity doesn't mean that people are as EVIL as possible. We don't think Atheists or non-Christians are as evil as they possibly could be. With Jesus, we agree that even evil people can do good things, such as giving bread to their children instead of stones and eggs instead of snakes. We have no issue with people being nice people. Doing nice things for others. Loving their enemies even. Forgiving etc. We also accept that at times Christians do horrible and evil things. We don't condone it but we acknowledge that such things happen.
Total Depravity means tainted by sin in every aspect of life. A good illustration I have used before is of the glass of water. Take a glass of pure water and add one drop of oil or ink to it. Does it turn the pure water totally into ink or oil? No. But it taints every droplet of water in the glass. The pure water becomes tainted. No one would drink it. The water becomes grey. Yet it doesn't become totally evil. Yet it is totally depraved.
Similarly, we say every human is totally depraved. Sin taints every aspect of our lives. Not that we become totally evil, but that we become such that we are no longer pure or holy. God won't drink us. God of course has a purifier. That was the cross and Jesus. Hence those who want to be holy or purified require Jesus.
What this means is that we don't think Atheists are totally evil. Not everyone is Hitler. (some people seem to be worse than others) Atheists and other non-Christians are able to make decent and reasonable decisions for themselves and for their children and others around them. Yet they remain tainted by sin and this impacts everything they do. Christians on the other hand, have been redeemed by Christ, the purifier. Yet this is firstly, a DECLARATION in heaven, and then secondly, a work in the person in life through the Spirit of God. Justification, followed by sanctification. And then glorification. Sanctification is the process of becoming purified on this earth. God works in us through his Word and His Spirit to make us holy on this earth. Yet, in this process, Christians sadly, continue to sin. But now they are no longer slaves to sin. And are progressing in their sanctification. Unless they are progressing, then without good fruit or good works happening, it is potentially true that their alleged conversion was more emotional or guilt manipulation or a figment of their imagination. This is why we should never try and manipulate people into the kingdom. And why such methodology actually does more harm for the church than good. Yet, it is true that the justified person is being sanctified in life, so that he or she can be glorified in heaven. In other words, sin is a reality in this world. It exists. We see it in sickness, in death, in the corruption, in our own hearts. Yet, in heaven, these things are no longer an issue since we have been glorified with Christ.
These things explain why atheists and other non-Christians can do good things and not murder people. It doesn't off course reflect what is in their hearts which may well want to do these things. It also explains why Christians, even those who have been born again, continue to sin. Yet the Christian is the person who is no longer slave to sin. Hence, why it is a bigger responsibility for him or her when they do sin. And why the world watches with glee when the church or Christians stuff up. Christians admit to a higher moral code. This makes them a target. A great motivator not to sin. The world doesn't need to target someone or a group who is not setting themselves as a model for others. Atheists will never need to worry while they maintain they only have one doctrine. Hence, why they avoid the inevitable worldview of their beliefs. They know they would become a target. So I guess that is a smart strategy.